Mobile communication system

ABSTRACT

A mobile communication system includes a plurality of eNBs that perform radio communication with an UE and an MCE that controls the eNBs. The MCE indicates an MBSFN subframe (MCE) serving as radio resources that transmit a reference signal for power measurement to the UE less frequently than normal to the eNB, the eNB, in addition to the MBSFN subframe (MCE) indicated by the MCE, designates the MBSFN subframe (eNB) serving as the radio resources that transmit a reference signal to the UE less frequently than normal, and in the MBSFN subframe (MCE) and the MBSFN subframe (eNB) the reference signal is transmitted to the UE. In this manner, the reference signal for measuring a power can be transmitted less frequently than normal, and a power consumption of the infrastructure can be reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/640,334 filed Oct. 10, 2012, the entire content of which isincorporated herein by reference. U.S. application Ser. No. 13/640,334is a National Phase of PCT/JP2011/002406 filed Apr. 25, 2011 and claimspriority to Japanese Patent Application Nos. 2010-103487 filed Apr. 28,2010 and 2010-223903 filed Oct. 1, 2010.

TECHNICAL FIELD

The present invention relates to a mobile communication system in whicha base station performs radio communication with a plurality of userequipments.

BACKGROUND ART

Commercial service of W-CDMA (Wideband Code division Multiple Access)system among so-called third-generation communication systems has beenoffered in Japan since 2001. In addition, HSDPA (High Speed DownlinkPacket Access) service for achieving higher-speed data transmissionusing a downlink has been offered by adding a channel for packettransmission (HS-DSCH: High Speed-Downlink Shared Channel) to thedownlink (dedicated data channel, dedicated control channel). Further,in order to increase the speed of data transmission in an uplinkdirection, service of an HSUPA (High Speed Uplink Packet Access) systemhas been offered. W-CDMA is a communication system defined by the 3GPP(3rd Generation Partnership Project) that is the standards organizationregarding the mobile communication system, where the specifications ofRelease 8 version are produced.

Further, 3GPP is studying new communication systems referred to as “longterm evolution (LTE)” regarding radio areas and “system architectureevolution (SAE)” regarding the overall system configuration including acore network (merely referred to as network as well) as communicationsystems independent of W-CDMA. In the LTE, an access scheme, a radiochannel configuration and a protocol are totally different from those ofthe current W-CDMA (HSDPA/HSUPA). For example, as to the access scheme,code division multiple access is used in the W-CDMA, whereas in the LTE,OFDM (Orthogonal Frequency Division Multiplexing) is used in a downlinkdirection and SC-FDMA (Single Career Frequency Division Multiple Access)is used in an uplink direction. In addition, the bandwidth is 5 MHz inthe W-CDMA, while in the LTE, the bandwidth can be selected from 1.4MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz for each base station.Further, differently from the W-CDMA, circuit switching is not providedbut a packet communication system is only provided in the LTE.

The LTE is defined as a radio access network independent of the W-CDMAnetwork because its communication system is configured with a new corenetwork different from a core network (GPRS) of the W-CDMA. Therefore,for differentiation from the W-CDMA communication system, a base stationthat communicates with a user equipment (UE) and a radio networkcontroller that transmits/receives control data and user data to/from aplurality of base stations are referred to as an eNB (E-UTRAN NodeB) andan EPC (Evolved Packet Core) (also referred to as access gateway (aGW:Access Gateway)), respectively, in the LTE communication system. Unicastservice and E-MBMS service (Evolved Multimedia Broadcast MulticastService) are provided in this LTE communication system. The E-MBMSservice is broadcast multimedia service, which is merely referred to asMBMS in some cases. Bulk broadcast contents such as news, weatherforecast and mobile broadcast are transmitted to a plurality of userequipments. This is also referred to as point to multipoint service.

Non-Patent Document 1 describes the current decisions by 3GPP regardingan overall architecture in the LTE system. The overall architecture(Chapter 4.6.1 of Non-Patent Document 1) is described with reference toFIG. 1. FIG. 1 is a diagram illustrating the configuration of the LTEcommunication system. With reference to FIG. 1, the E-UTRAN (EvolvedUniversal Terrestrial Radio Access) is composed of one or a plurality ofbase stations 102, provided that a control protocol (for example, RRC(Radio Resource Management)) and a user plane (for example, PDCP: PacketData Convergence Protocol, RLC: Radio Link Control, MAC: Medium AccessControl, and PHY: Physical Layer) for a user equipment 101 areterminated in the base station 102. The base stations 102 performscheduling and transmission of paging signal (also referred to as pagingmessages) notified from an MME 103 (Mobility Management Entity). Thebase stations 102 are connected to each other by means of an X2interface. In addition, the base stations 102 are connected to an EPC(Evolved Packet Core) by means of an S1 interface, more specifically,connected to the MME 103 (Mobility Management Entity) by means of anS1_MME interface and connected to an S-GW 104 (Serving Gateway) by meansof an S1_U interface. The MME 103 distributes the paging signaling tomultiple or a single base station 102. In addition, the MME 103 performsmobility control of an idle state. When the user equipment is in theidle state and an active state, the MME 103 manages a list of trackingareas. The S-GW 104 transmits/receives user data to/from one or aplurality of base stations 102. The S-GW 104 serves as a local mobilityanchor point in handover between base stations. Moreover, there isprovided a P-GW (PDN Gateway), which performs per-user packet filteringand UE-ID address allocation.

The control protocol RRC between the user equipment 101 and the basestation 102 performs broadcast, paging, RRC connection management andthe like. The states of the base station and the user equipment in RRCare classified into RRC_Idle and RRC_CONNECTED. In RRC_IDLE, PLMN(Public Land Mobile Network) selection, system information (SI)broadcast, paging, cell reselection, mobility and the like areperformed. In RRC_CONNECTED, the user equipment has RRC connection, iscapable of transmitting/receiving data to/from a network, and performs,for example, handover (HO) and measurement of a neighbor cell. RRC_IDLEis also merely referred to as IDLE or an idle state. RRC_CONNECTED isalso merely referred to as CONNECTED.

The current decisions by 3GPP regarding the frame configuration in theLTE system are described in Non-Patent Document 1 (Chapter 5).Description is given with reference to FIG. 2. FIG. 2 is a diagramillustrating the configuration of a radio frame used in the LTEcommunication system. With reference to FIG. 2, one radio frame is 10ms. The radio frame is divided into ten equally sized subframes. Thesubframe is divided into two equally sized slots. The first and sixthsubframes contain a downlink synchronization signal (SS) per each radioframe. The synchronization signals are classified into a primarysynchronization signal (P-SS) and a secondary synchronization signal(S-SS). Multiplexing of channels for multimedia broadcast multicastservice single frequency network (MBSFN) and for non-MBSFN is performedon a per-subframe basis. MBSFN Transmission is a simulcast transmissiontechnique realized by simultaneous transmission of the same waveformsfrom a plurality of cells. MBSFN transmission from a plurality of cellsin an MBSFN area appears as one transmission by a user equipment. MBSFNis a network that supports the MBSFN transmission. Hereinafter, asubframe for MBSFN transmission is referred to as an MBSFN subframe.Non-Patent Document 2 describes a signaling example when MBSFN subframesare allocated. FIG. 3 is a diagram illustrating the configuration of theMBSFN frame. With reference to FIG. 3, the MBSFN subframes are allocatedfor each MBSFN frame. The MBSFN frame is repeated in a radio FrameAllocation Period. An MBSFN subframe is a subframe allocated for MBSFNin a radio frame defined by the radio frame allocation period and aradio Frame Allocation Offset, and is a subframe to transmit multimediadata. A radio frame that satisfies the following equation (1) is a radioframe including the MBSFN subframe.SFN Mod radioFrameAllocationPeriod=radioFrameAllocationOffset  Equation(1)

Allocation of the MBSFN subframe is performed by 6 bits. The leftmostbit defines MBSFN allocation of a second (#1) subframe. A second bitdefines MBSFN allocation of a third subframe (#2), a third bit definesMBSFN allocation of a fourth subframe (#3), a fourth bit defines MBSFNallocation of a seventh subframe (#6), a fifth bit defines MBSFNallocation of an eighth subframe (#7), and a sixth bit defines MBSFNallocation of an ninth subframe (#8). When the bit shows “1”, it isshown that a corresponding subframe is allocated for MBSFN.

Non-Patent Document 1 describes the current decisions by 3GPP regardingthe channel configuration in the LTE system. It is assumed that the samechannel configuration is used in a CSG cell (Closed Subscriber Groupcell) as that of a non-CSG cell. A physical channel (Chapter 5 ofNon-Patent Document 1) is described with reference to FIG. 4. FIG. 4 isa diagram illustrating physical channels used in the LTE communicationsystem. With reference to FIG. 4, a physical broadcast channel (PBCH)401 is a downlink channel transmitted from the base station 102 to theuser equipment 101. A BCH transport block is mapped to four subframeswithin a 40 ms interval. There is no explicit signaling indicating 40 mstiming. A physical control format indicator channel (PCFICH) 402 istransmitted from the base station 102 to the user equipment 101. ThePCFICH notifies the number of OFDM symbols used for PDCCHs from the basestation 102 to the user equipment 101. The PCFICH is transmitted in eachsubframe. A physical downlink control channel (PDCCH) 403 is a downlinkchannel transmitted from the base station 102 to the user equipment 101.The PDCCH notifies the resource allocation, HARQ information related toDL-SCH (downlink shared channel that is one of the transport channelsshown in FIG. 5) and the PCH (paging channel that is one of thetransport channels shown in FIG. 5). The PDCCH carries an uplinkscheduling grant. The PDCCH carries ACK/Nack that is a response signalto uplink transmission. The PDCCH is also referred to as an L1/L2control signal as well. A physical downlink shared channel (PDSCH) 404is a downlink channel transmitted from the base station 102 to the userequipment 101. A DL-SCH (downlink shared channel) that is a transportchannel and a PCH that is a transport channel are mapped to the PDSCH. Aphysical multicast channel (PMCH) 405 is a downlink channel transmittedfrom the base station 102 to the user equipment 101. A multicast channel(MCH) that is a transport channel is mapped to the PMCH.

A physical uplink control channel (PUCCH) 406 is an uplink channeltransmitted from the user equipment 101 to the base station 102. ThePUCCH carries ACK/Nack that is a response signal to downlinktransmission. The PUCCH carries a channel quality indicator (CQI)report. The CQI is quality information indicating the quality ofreceived data or channel quality. In addition, the PUCCH carries ascheduling request (SR). A physical uplink shared channel (PUSCH) 407 isan uplink channel transmitted from the user equipment 101 to the basestation 102. A UL-SCH (uplink shared channel that is one of thetransport channels shown in FIG. 5) is mapped to the PUSCH. A physicalhybrid ARQ indicator channel (PHICH) 408 is a downlink channeltransmitted from the base station 102 to the user equipment 101. ThePHICH carries ACK/Nack that is a response to uplink transmission. Aphysical random access channel (PRACH) 409 is an uplink channeltransmitted from the user equipment 101 to the base station 102. ThePRACH carries a random access preamble.

A downlink reference signal is a known symbol serving as a mobilecommunication system. The physical layer measurement objects of a userequipment include, for example, reference symbol received power (RSRP).

The transport channel (Chapter 5 of Non-Patent Document 1) is describedwith reference to FIG. 5. FIG. 5 is a diagram illustrating transportchannels used in the LTE communication system. Part [A] of FIG. 5 showsmapping between a downlink transport channel and a downlink physicalchannel. Part [B] of FIG. 5 shows mapping between an uplink transportchannel and an uplink physical channel. A broadcast channel (BCH) isbroadcast to the entire base station (cell) regarding the downlinktransport channel. The BCH is mapped to the physical broadcast channel(PBCH). Retransmission control according to a HARQ (Hybrid ARQ) isapplied to a downlink shared channel (DL-SCH). Broadcast to the entirebase station (cell) is enabled. The DL-SCH supports dynamic orsemi-static resource allocation. The semi-static resource allocation isalso referred to as persistent scheduling. The DL-SCH supports DRX(Discontinuous reception) of a user equipment for enabling the userequipment to save power. The DL-SCH is mapped to the physical downlinkshared channel (PDSCH). The paging channel (PCH) supports DRX of theuser equipment for enabling the user equipment to save power. Broadcastto the entire base station (cell) is required. The PCH is mapped to aphysical resource such as the physical downlink shared channel (PDSCH)that can be used dynamically for traffic or a physical resource such asthe physical downlink control channel (PDCCH) of the other controlchannel. The multicast channel (MCH) is used for broadcast to the entirebase station (cell). The MCH supports SFN combining of MBMS service(MTCH and MCCH) in multi-cell transmission. The MCH supports semi-staticresource allocation. The MCH is mapped to the PMCH.

Retransmission control according to an HARQ (Hybrid ARQ) is applied toan uplink shared channel (UL-SCH). The DL-SCH supports dynamic orsemi-static resource allocation. The UL-SCH is mapped to the physicaluplink shared channel (PUSCH). A random access channel (RACH) shown inpart [B] of FIG. 5 is limited to control information. There is acollision risk. The RACH is mapped to the physical random access channel(PRACH).

The HARQ is described. The HARQ is the technique for improving thecommunication quality of a channel by combination of automatic repeatrequest and forward error correction. The HARQ has an advantage thaterror correction functions effectively by retransmission even for achannel whose communication quality changes. In particular, it is alsopossible to achieve further quality improvement in retransmissionthrough combination of the reception results of the first transmissionand the reception results of the retransmission. An example of theretransmission method is described. In a case where the receiver failsto successfully decode the received data (in a case where a cyclicredundancy check (CRC) error occurs (CRC=NG)), the receiver transmits“Nack” to the transmitter. The transmitter that has received “Nack”retransmits the data. In a case where the receiver successfully decodesthe received data (in a case where a CRC error does not occur (CRC=OK)),the receiver transmits “AcK” to the transmitter. The transmitter thathas received “Ack” transmits the next data. Examples of the HARQ systeminclude “chase combining”. In chase combining, the same data sequence istransmitted in the first transmission and retransmission, which is thesystem for improving gains by combining the data sequence of the firsttransmission and the data sequence of the retransmission inretransmission. This is based on the idea that correct data is partiallyincluded even if the data of the first transmission contains an error,and highly accurate data transmission is enabled by combining thecorrect portions of the first transmission data and the retransmissiondata. Another example of the HARQ system is IR (incremental redundancy).The IR is aimed to increase redundancy, where a parity bit istransmitted in retransmission to increase the redundancy by combiningthe first transmission and retransmission, to thereby improve thequality by an error correction function.

A logical channel (Chapter 6 of Non-Patent Document 1) is described withreference to FIG. 6. FIG. 6 is a diagram illustrating logical channelsused in an LTE communication system. Part [A] of FIG. 6 shows mappingbetween a downlink logical channel and a downlink transport channel.Part [B] of FIG. 6 shows mapping between an uplink logical channel andan uplink transport channel. A broadcast control channel (BCCH) is adownlink channel for broadcast system control information. The BCCH thatis a logical channel is mapped to the broadcast channel (BCH) ordownlink shared channel (DL-SCH) that is a transport channel. A pagingcontrol channel (PCCH) is a downlink channel for transmitting pagingsignals. The PCCH is used when the network does not know the celllocation of a user equipment. The PCCH that is a logical channel ismapped to the paging channel (PCH) that is a transport channel. A commoncontrol channel (CCCH) is a channel for transmission control informationbetween user equipments and a base station. The CCCH is used in a casewhere the user equipments have no RRC connection with the network. Indownlink, the CCCH is mapped to the downlink shared channel (DL-SCH)that is a transport channel. In uplink, the CCCH is mapped to the uplinkshared channel uplink shared channel (UL-SCH) that is a transportchannel.

A multicast control channel (MCCH) is a downlink channel forpoint-to-multipoint transmission. The MCCH is a channel used fortransmission of MBMS control information for one or several MTCHs from anetwork to a user equipment. The MCCH is a channel used only by a userequipment during reception of the MBMS. The MCCH is mapped to thedownlink shared channel (DL-SCH) or multicast channel (MCH) that is atransport channel. A dedicated control channel (DCCH) is a channel thattransmits dedicated control information between a user equipment and anetwork. The DCCH is mapped to the uplink shared channel (UL-SCH) inuplink and mapped to the downlink shared channel (DL-SCH) in downlink. Adedicated traffic channel (DTCH) is a point-to-point communicationchannel for transmission of user information to a dedicated userequipment. The DTCH exists in uplink as well as downlink. The DTCH ismapped to the uplink shared channel (UL-SCH) in uplink and mapped to thedownlink shared channel (DL-SCH) in downlink. A multicast trafficchannel (MTCH) is a downlink channel for traffic data transmission froma network to a user equipment. The MTCH is a channel used only by a userequipment during reception of the MBMS. The MTCH is mapped to thedownlink shared channel (DL-SCH) or multicast channel (MCH).

GCI represents a global cell identity. In the LTE and UMTS (UniversalMobile Telecommunication System), a CSG cell (Closed Subscriber Groupcell) is introduced. The CSG is described below (Chapter 3.1 ofNon-Patent Document 3). The CSG (Closed Subscriber Group) is a cell inwhich subscribers who are allowed to use are specified by an operator(cell for specific subscribers). The specific subscribers are allowed tomake access one or more E-UTRAN cells of a PLMN (public land mobilenetwork). One or more E-UTRAN cells in which the specific subscribersare allowed to make access are referred to as “CSG cell(s)”. Note thataccess is limited in the PLMN. The CSG cell is part of the PLMN thatbroadcasts a specific CSG identity (CSG ID, CSG-ID). The authorizedmembers of the subscriber group who have registered in advance accessthe CSG cells using the CSG-ID that is the access permissioninformation.

The CSG-ID is broadcast by the CSG cell or cells. A plurality of CSG-IDsexist in a mobile communication system. The CSG-IDs are used by userequipments (UEs) for making access from CSG-related members easier. Thelocations of user equipments are traced based on an area composed of oneor more cells. The locations are traced for enabling tracing of thelocations of user equipments and calling (calling of user equipments)even in an idle state. An area for tracing locations of user equipmentsis referred to as a tracking area. A CSG whitelist is a list stored inthe USIM (Universal Subscriber Identity Module) in which all CSG IDs ofthe CSG cells to which the subscribers belong are recorded. The CSGwhitelist is also referred to as an allowed CSG ID list in some cases.

A “suitable cell” is described below (Chapter 4.3 of Non-Patent Document3). The “suitable cell” is a cell on which a UE camps (Camp ON) toobtain normal service. Such a cell satisfies a condition in which (1)the cell is part of a selected PLMN, a registered PLMN, or a PLMN of“Equivalent PLMN list”, (2) the cell further satisfies the followingconditions by the latest information provided by an NAS (non-accessstratum), and (a) the cell is not a barred cell. (b) The cell is notpart of an “LAs barred for roaming” list, but part of at least onetracking area (TA). In this case, the cell must fulfill the (1), (c) thecell satisfies a cell selection criteria, (d) the cell, that isspecified as a CSG cell by system information (SI) is part of a “CSGwhitelist” of the UE (included in the CSG whitelist of the UE).

An “acceptable cell” is described below (Chapter 4.3 of Non-PatentDocument 3). This is the cell on which a UE camps to obtain limitedservice (emergency calls). Such a cell shall fulfill all the followingrequirements. That is, the minimum required set for initiating anemergency call in an E-UTRAN network are as follows. (1) the cell is nota barred cell. (2) the cell shall fulfill the cell selection criteria.

Camping on a cell represents the state where a UE has completed the cellselection/reselection process and the UE has selected a cell formonitoring the system information and paging information.

3GPP is studying base stations referred to as Home-NodeB (Home-NB, HNB)and Home-eNodeB (Home-eNB, HeNB). HNB/HeNB is a base station for, forexample, household, corporation or commercial access service inUTRAN/E-UTRAN. Non-Patent Document 4 discloses three different modes ofthe access to the HeNB and HNB. Those are an open access mode, a closedaccess mode and a hybrid access mode. The respective modes have thefollowing characteristics. In the open access mode, the HeNB and HNB areoperated as a normal cell of a normal operator. In the closed accessmode, the HeNB and HNB are operated as a CSG cell. The CSG cell is acell where only CSG members are allowed access. In the hybrid accessmode, non-CSG members are allowed to access at the same time. In otherwords, a cell in the hybrid access mode (also referred to as hybridcell) is the cell that supports both the open access mode and the closedaccess mode.

In 3GPP, as Release 10, the standards of “long term evolution advanced”(LTE-A) are being established (Non-Patent Document 6 and Non-PatentDocument 7).

In the LTE-A system, it is examined that a relay (relay node (RN)) issupported to obtain a high communication speed, a high throughput atcell edge, a new coverage area and the like. The relay node iswirelessly connected to a radio access network through a donor cell(donor eNB or DeNB). Within the range of the donor cell, a link from anNW to a relay node shares the same frequency band as that of a link froma network to a UE. In this case, the UE of Release 8 can also beconnected to the donor cell. A link between a donor cell and a relaynode is referred to as a backhaul link, and a link between a relay nodeand a UE is referred to as an access link.

As a backhaul link multiplexing method in FDD, transmission from a DeNBto an RN is performed in a downlink (DL) frequency band, transmissionfrom an RN to a DeNB is an uplink (UL) frequency band. As a resourcesplitting method in a relay, a link from a DeNB to an RN and a link froman RN to a UE are time-multiplexed in one frequency band, and a linkfrom an RN to a DeNB and a link from a UE to an RN are time-multiplexedin one frequency band. In this manner, in the relay, transmission of therelay can be prevented from interfering with reception of its own relay.

PRIOR ART DOCUMENTS Non-Patent Documents

-   Non-Patent Document 1: 3GPP TS36. 300 V9. 2. 0 Chapter 4. 6. 1,    Chapter 4. 6. 2, Chapter 5, Chapter 6, and Chapter 10.7-   Non-Patent Document 2: 3GPP TS36.331 V9.1.0-   Non-Patent Document 3: 3GPP TS36. 304 V9.1.0 Chapter 3.1, Chapter    4.3 and Chapter 5.2.4-   Non-Patent Document 4: 3GPP S1-083461-   Non-Patent Document 5: 3GPP R2-082899-   Non-Patent Document 6: 3GPP TR 36. 814 V9. 0. 0-   Non-Patent Document 7: 3GPP TR 36. 912 V9. 0. 0-   Non-Patent Document 8: 3GPP R1-095011-   Non-Patent Document 9: 3GPP TS36.443 V9.0.0-   Non-Patent Document 10: 3GPP R1-100275-   Non-Patent Document 11: 3GPP R1-101620

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

In 3GPP, lower power consumption (energy saving) of an infrastructure isbeing discussed. It is examined that lower power consumption of a basestation can be achieved by reducing transmission time of CRS by using anMBSFN subframe.

It is an object of the present invention to provide a mobilecommunication system that can efficiently reduce a power consumption ofan infrastructure.

Means for Solving the Problems

The present invention relates to a mobile communication system includinga plurality of base stations that perform radio communication with userequipments and a radio network controller that controls the plurality ofbase stations, wherein the radio network controller indicates alow-frequency resource that is a radio resource for transmitting areference signal for measuring a power to the user equipments lessfrequently than normal to the base stations, the base station indicates,in addition to the low-frequency resource indicated by the radio networkcontroller, a low-frequency resource that is a radio resource fortransmitting the reference signal to the user equipment less frequentlythan normal, and the base station transmits the reference signal to theuser equipment less frequently than normal in the low-frequency resourceindicated by the radio network controller and the low-frequency resourceadditionally designated by the base station itself.

Effects of the Invention

According to the present invention, in addition to the radio resourceindicated by the radio network controller, in the radio resourcedesignated by the base station itself, the reference signal formeasuring a power can be transmitted less frequently than normal, and apower consumption of the infrastructure can be reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the configuration of an LTEcommunication system.

FIG. 2 is a diagram illustrating the configuration of a radio frame usedin the LTE communication system.

FIG. 3 is a diagram illustrating the configuration of the MBSFN(Multimedia Broadcast multicast service Single Frequency Network) frame.

FIG. 4 is a diagram illustrating physical channels used in the LTEcommunication system.

FIG. 5 is a diagram illustrating transport channels used in the LTEcommunication system.

FIG. 6 is a diagram illustrating logical channels used in the LTEcommunication system.

FIG. 7 is a block diagram showing the overall configuration of a mobilecommunication system currently under discussion of 3GPP.

FIG. 8 is a block diagram showing the configuration of a user equipment71 according to the present invention.

FIG. 9 is a block diagram showing the configuration of a base station 72according to the present invention.

FIG. 10 is a block diagram showing the configuration of an MME accordingto the present invention.

FIG. 11 is a block diagram showing the configuration of a HeNBGWaccording to the present invention.

FIG. 12 is a flowchart showing an outline of cell search performed by auser equipment (UE) in the LTE communication system.

FIG. 13 is a diagram illustrating a theoretical architecture of E-MBMScurrently under discussion of 3GPP.

FIG. 14 is a diagram illustrating a sequence of a mobile communicationsystem when the solution of the first embodiment is used.

FIG. 15 is a location diagram illustrating a problem of a firstmodification of the first embodiment.

FIG. 16 is a diagram illustrating a sequence of a mobile communicationsystem when the solution of the first modification of the firstembodiment is used.

FIG. 17 is a diagram illustrating a sequence of a mobile communicationsystem for explaining a problem of a second modification of the firstembodiment.

FIG. 18 is a diagram illustrating a sequence of a mobile communicationsystem when a solution of the second modification of the firstembodiment is used.

FIG. 19 is a specific example of information of a priority order when athird modification of the first embodiment is used.

FIG. 20 is a diagram illustrating a sequence of a mobile communicationsystem when a solution of a third modification of the first embodimentis used.

FIG. 21 is a diagram illustrating a sequence of a mobile communicationsystem when a solution of a fifth modification of the first embodimentis used.

FIG. 22 is a generation pattern of paging occasion currently underdiscussion of 3GPP.

FIG. 23 is a diagram illustrating a sequence of a mobile communicationsystem when a combination of the third embodiment and the firstmodification of the first embodiment is used.

FIG. 24 is a diagram illustrating a sequence of a mobile communicationsystem when a solution of a first modification of the third embodimentis used.

FIG. 25 is a diagram illustrating a sequence of a mobile communicationsystem when a solution of a second modification of the third embodimentis used.

EMBODIMENTS FOR CARRYING OUT THE INVENTION First Embodiment

FIG. 7 is a block diagram showing an overall configuration of an LTEmobile communication system, which is currently under discussion of3GPP. In current 3GPP, an overall configuration of a system including aCSG (Closed Subscriber Group) cell (Home-eNodeB (Home-eNB, HeNB) ofe-UTRAN and Home-NB (HNB) of UTRAN) and a non-CSG cell (eNodeB (eNB) ofe-UTRAN, NodeB (NB) of UTRAN and BSS of GERAN) is examined. For thee-UTRAN, the configuration shown in FIG. 7 is proposed (Chapter 4.6.1.of Non-Patent Document 1).

FIG. 7 is described. A user equipment (UE) 71 performstransmission/reception to/from a base station 72. The base stations 72are classified into an eNB 72-1 and Home-eNBs 72-2. The eNB 72-1 isconnected to MMEs 73 through S1 interfaces, and control information iscommunicated between the eNB and the MMEs. A plurality of MMEs 73 may beconnected to one eNB 72-1. The eNBs are connected to each other by meansof an X2 interface, and control information is communicated between theeNBs.

The Home-eNB 72-2 is connected to the MME 73 by means of the S1interface, and control information is communicated between the Home-eNBand the MME. A plurality of Home-eNBs are connected to one MME.Alternatively, the Home-eNBs 72-2 are connected to the MMEs 73 through aHeNBGW (Home-eNB Gateway) 74. The Home-eNBs 72-2 are connected to theHeNBGW 74 by means of the S1 interfaces, and the HeNBGW 74 is connectedto the MMEs 73 through an S1 interface. One or a plurality of Home-eNBs72-2 are connected to one HeNBGW 74, and information is communicatedtherebetween through the S1 interface. The HeNBGW 74 is connected to oneor a plurality of MMEs 73, and information is communicated therebetweenthrough the S1 interface.

Further, 3GPP is currently studying the configuration below. The X2interface between the Home-eNBs 72-2 is not supported. The HeNBGW 74appears to the MME 73 as the eNB 72-1. The HeNBGW 74 appears to theHome-eNB 72-2 as the MME 73. The S1 interface between the Home-eNB 72-2and the EPC is the same irrespective of whether or not the Home-eNB 72-2is connected to the EPC through the HeNBGW 74. The mobility to theHome-eNB 72-2 or the mobility from the Home-eNB 72-2 that spans the MMEs73 is not supported. The Home-eNB 72-2 supports a single cell.

FIG. 8 is a block diagram showing the configuration of the userequipment (equipment 71 of FIG. 7) according to the present invention.The transmission process of the user equipment shown in FIG. 8 isdescribed. First, a transmission data buffer unit 803 stores the controldata from a protocol processing unit 801 and the user data from anapplication unit 802. The data stored in the transmission data bufferunit 803 is transmitted to an encoding unit 804 and is subjected toencoding process such as error correction. There may exist the dataoutput from the transmission data buffer unit 803 directly to amodulating unit 805 without encoding process. The data encoded by theencoding unit 804 is modulated by the modulating unit 805. The modulateddata is output to a frequency converting unit 806 after being convertedinto a baseband signal, and then is converted into a radio transmissionfrequency. After that, a transmission signal is transmitted from anantenna 807 to a base station 72. A user equipment 71 executes thereception process as follows. The antenna 807 receives the radio signalfrom the base station 72. The received signal is converted from a radioreception frequency to a baseband signal by the frequency convertingunit 806 and is then demodulated by a demodulating unit 808. Thedemodulated data is transmitted to a decoding unit 809 and is subjectedto decoding process such as error correction. Among the pieces ofdecoded data, the control data is transmitted to the protocol processingunit 801, while the user data is transmitted to the application unit802. A series of process of the user equipment is controlled by acontrol unit 810. This means that, though not shown, the control unit810 is connected to the respective units (801 to 809).

FIG. 9 is a block diagram showing the configuration of the base station(base station 72 of FIG. 7) according to the present invention. Thetransmission process of the base station shown in FIG. 9 is described.An EPC communication unit 901 performs data transmission/receptionbetween the base station 72 and the EPCs (such as MME 73 and HeNBGW 74).A communication with another base station unit 902 performs datatransmission/reception to/from another base station. The X2 interfacebetween the Home-eNBs 72-2 is not intended to be supported, andaccordingly, it is conceivable that the communication with another basestation unit 902 may not exist in the Home-eNB 72-2. The EPCcommunication unit 901 and the communication with another base stationunit 902 respectively transmit/receive information to/from the protocolprocessing unit 903. The control data from the protocol processing unit903, and the user data and control data from the EPC communication unit901 and the communication with another base station unit 902 are storedin the transmission data buffer unit 904. The data stored in thetransmission data buffer unit 904 is transmitted to an encoding unit 905and is then subjected to encoding process such as error correction.There may exist the data output from the transmission data buffer unit904 directly to a modulating unit 906 without encoding process. Theencoded data is modulated by the modulating unit 906. The modulated datais output to a frequency converting unit 907 after being converted intoa baseband signal, and is then converted into a radio transmissionfrequency. After that, a transmission signal is transmitted from anantenna 908 to one or a plurality of user equipments 71. While, thereception process of the base station 72 is executed as follows. A radiosignal from one or a plurality of user equipments 71 is received by theantenna 908. The received signal is converted from a radio receptionfrequency into a baseband signal by the frequency converting unit 907,and is then demodulated by a demodulating unit 909. The demodulated datais transmitted to a decoding unit 910 and is then subjected to decodingprocess such as error correction. Among the pieces of decoded data, thecontrol data is transmitted to the protocol processing unit 903, EPCcommunication unit 901, or communication with another base station unit902, while the user data is transmitted to the EPC communication unit901 and communication with another base station unit 902. A series ofprocess by the base station 72 is controlled by a control unit 911. Thismeans that, though not shown, the control unit 911 is connected to therespective units (901 to 910).

The functions of the Home-eNB 72-2 currently under discussion of 3GPPare described below (Chapter 4.6.2 of Non-Patent Document 1). TheHome-eNBs 72-2 has the same function as that of the eNB 72-1. Inaddition, when the Home-eNB 72-2 is connected to the HeNBGW 74, theHome-eNB 72-2 has the following function. The Home-eNB 72-2 has afunction of discovering a suitable serving HeNBGW 74. In a case wherethe Home-eNB 72-2 is connected to one HeNBGW 74 only, that is, in a caseof connection to the HeNBGW 74, the Home-eNB 72-2 does not use the Flexfunction of the S1 interface. When the Home-eNB 72-2 is connected to theHeNBGW 74, it is not simultaneously connected to another HeNBGW 74 oranother MME 73. The TAC and PLMN ID used by the Home-eNB 72-2 aresupported by the HeNBGW 74. When the Home-eNB 72-2 is connected to theHeNBGW 74, selection of the MME 73 at “UE attachment” is performed bythe HeNBGW 74 instead of the Home-eNB 72-2. The Home-eNB 72-2 may bedeployed without network planning. Accordingly, the Home-eNB 72-2 may bemoved from one geographical area to another geographical area.Accordingly, the Home-eNB 72-2 may be required to be connected to adifferent HeNBGW 74 depending on its location.

FIG. 10 is a block diagram showing the configuration of an MME (MobilityManagement Entity) according to the present invention. A PDN GWcommunication unit 1001 performs data transmission/reception between anMME 73 and a PDN GW. A base station communication unit 1002 performsdata transmission/reception between the MME 73 and the base station 72by means of the S1 interface. In the case where the data received fromthe PDN GW is user data, the user data is transmitted from the PDN GWcommunication unit 1001 to the base station communication unit 1002through a user plane processing unit 1003 and is then transmitted to oneor a plurality of base stations 72. In the case where the data receivedfrom the base station 72 is user data, the user data is transmitted fromthe base station communication unit 1002 to the PDN GW communicationunit 1001 through the user plane processing unit 1003 and is thentransmitted to the PDN GW.

In the case where the data received from the PDN GW is control data, thecontrol data is transmitted from the PDN GW communication unit 1001 to acontrol plane control unit 1005. In the case where the data receivedfrom the base station 72 is control data, the control data istransmitted from the base station communication unit 1002 to the controlplane control unit 1005. A HeNBGW communication unit 1004 is provided inthe case where the HeNBGW 74 is provided, which performs datatransmission/reception by means of the interface (IF) between the MME 73and the HeNBGW 74 according to an information type. The control datareceived from the HeNBGW communication unit 1004 is transmitted from theHeNBGW communication unit 1004 to the control plane control unit 1005.The processing results of the control plane control unit 1005 aretransmitted to the PDN GW through the PDN GW communication unit 1001.The processing results of the control plane control unit 1005 aretransmitted to one or a plurality of base stations 72 by means of the S1interface through the base station communication unit 1002, and aretransmitted to one or a plurality of HeNBGWs 74 through the HeNBGWcommunication unit 1004.

The control plane control unit 1005 includes an NAS security unit1005-1, an SAE bearer control unit 1005-2 and an idle state mobilitymanaging unit 1005-3, and performs overall process for the controlplane. The NAS security unit 1005-1 provides security or the like of anNAS (Non-Access Stratum) message. The SAE bearer control unit 1005-2manages, for example, an SAE (System Architecture Evolution) bearer. Theidle state mobility managing unit 1005-3 performs, for example, mobilitymanagement of an idle state (LTE-IDLE state, which is merely referred toas idle as well), generation and control of paging signaling in an idlestate, addition, deletion, update and search of a tracking area (TA) ofone or a plurality of user equipments 71 being served thereby, andtracking area list (TA List) management. The MME begins a pagingprotocol by transmitting a paging message to the cell belonging to atracking area (TA) in which the UE is registered. The idle statemobility managing unit 1005-3 may manage the CSG of the Home-eNBs 72-2to be connected to the MME, CSG-IDs and a whitelist. In the CSG-IDmanagement, the relationship between a user equipment corresponding tothe CSG-ID and the CSG cell is managed (added, deleted, updated orsearched). For example, it may be the relationship between one or aplurality of user equipments whose user access registration has beenperformed with a CSG-ID and the CSG cells belonging to this CSG-ID. Inthe whitelist management, the relationship between the user equipmentand the CSG-ID is managed (added, deleted, updated or searched). Forexample, one or a plurality of CSG-IDs with which user registration hasbeen performed by a user equipment may be stored in the whitelist. Theabove-mentioned management related to the CSG may be performed byanother part of the MME 73. A series of process by an MME 73 iscontrolled by a control unit 1006. This means that, though not shown,the control unit 1006 is connected to the respective units (1001 to1005).

The function of the MME 73 currently under discussion of 3GPP isdescribed below (Chapter 4.6.2 of Non-Patent Document 1). The MME 73performs access control for one or a plurality of user equipments beingmembers of CSGs (Closed Subscriber Groups). The execution of pagingoptimization is recognized as an option.

FIG. 11 is a block diagram showing the configuration of the HeNBGWaccording to the present invention. An EPC communication unit 1101performs data transmission/reception between the HeNBGW 74 and the MME73 by means of the S1 interface. A base station communication unit 1102performs data transmission/reception between the HeNBGW 74 and theHome-eNB 72-2 by means of the S1 interface. A location processing unit1103 performs the process of transmitting, to a plurality of Home-eNBs,the registration information or the like among the data transmitted fromthe MME 73 through the EPC communication unit 1101. The data processedby the location processing unit 1103 is transmitted to the base stationcommunication unit 1102 and is transmitted to one or a plurality ofHome-eNBs 72-2 through the S1 interface. The data only caused to passthrough (to be transparent) without requiring the process by thelocation processing unit 1103 is passed from the EPC communication unit1101 to the base station communication unit 1102, and is transmitted toone or a plurality of Home-eNBs 72-2 through the S1 interface. A seriesof process by the HeNBGW 74 is controlled by a control unit 1104. Thismeans that, though not shown, the control unit 1104 is connected to therespective units (1101 to 1103).

The function of the HeNBGW 74 currently under discussion of 3GPP isdescribed below (Chapter 4.6.2 of Non-Patent Document 1). The HeNBGW 74relays an S1 application. The HeNBGW 74 terminates the S1 applicationthat is not associated with the user equipment 71 though it is a part ofthe procedures of the MME 73 toward the Home-eNB 72-2. When the HeNBGW74 is deployed, the procedure that is not associated with the userequipment 71 is communicated between the Home-eNB 72-2 and the HeNBGW 74and between the HeNBGW 74 and the MME 73. The X2 interface is not setbetween the HeNBGW 74 and another node. The execution of pagingoptimization is recognized as an option.

Next, an example of a typical cell search method in a mobilecommunication system is described. FIG. 12 is a flowchart showing anoutline from cell search to an idle state operation performed by a userequipment (UE) in the LTE communication system. When the cell search isstarted by the user equipment, in Step ST1201, the slot timing and frametiming are synchronized by a primary synchronization signal (P-SS) and asecondary synchronization signal (S-SS) transmitted from a neighbor basestation. Synchronization codes, which correspond to PCIs (Physical CellIdentities) assigned per cell one by one, are assigned to thesynchronization signals (SS) including the P-SS and S-SS. The number ofPCIs is currently studied in 504 ways, and these 504 ways of PCIs areused for synchronization, and the PCIs of the synchronized cells aredetected (specified). Next, in Step ST1202, a reference signal RS(cell-specific Reference Signal: CRS), which is transmitted from thebase station per cell, is detected and the received power (also referredto as an RSRP) is measured. The code corresponding to the PCI one by oneis used for the reference signal RS, and separation from the other cellsis enabled by correlation using the code. The code for RS of the cell isderived from the PCI specified in Step ST1201, which makes it possibleto detect the RS and measure the RS received power. Next, in StepST1203, the cell having the best RS reception quality (for example, cellhaving the highest RS received power; best cell) is selected from one ormore cells that have been detected up to Step ST1202. In Step ST1204,next, the PBCH of the best cell is received, and the BCCH that is thebroadcast information is obtained. An MIB (Master Information Block)containing the cell configuration information is mapped on the BCCH overthe PBCH. Examples of the MIB information include the DL (down link)system bandwidth (also referred to as transmission bandwidthconfiguration: dl-bandwidth), transmission antenna number and SFN(System Frame Number).

In Step ST1205, next, the DL-SCH of the cell is received based on thecell configuration information of the MIB, to thereby obtain an SIB(System Information Block) 1 of the broadcast information BCCH. The SIB1contains the information regarding access to the cell, informationrelated to cell selection and scheduling information of other SIB (SIBk;k is an integer that satisfies k≥2). In addition, the SIB1 contains aTAC (Tracking Area Code). In Step ST1206, next, the user equipmentcompares the TAC received in Step ST1205 with the TAC that has beenalready possessed in a TA (Tracking Area) list by the user equipment. Ina case where the TAC received in Step ST 1205 is identical to the TACincluded in the TA list as a result of comparison, the user equipmententers an idle state operation in the cell. In the comparison, when theTAC received in Step ST1205 is not included in the TA list, the userequipment requests a core network (EPC) (including the MME or the like)to change the TA through the cell to perform TAU (Tracking Area Update).The core network updates the TA list based on an identification number(such as a UE-ID) of the user equipment transmitted from the userequipment together with a TAU request signal. The core network transmitsthe updated TA list to the user equipment. The user equipment rewrites(updates) the TAC list possessed by the user equipment with the receivedTA list. After that, the user equipment enters the idle state operationin the cell.

In the LTE and UMTS (Universal Mobile Telecommunication System), theintroduction of a CSG (Closed Subscriber Group) cell is studied. Asdescribed above, access is allowed for only one or a plurality of userequipments registered with the CSG cell. The CSG cell and one or aplurality of user equipments registered with the CSG cell constitute oneCSG. A specific identification number referred to as CSG-ID is added tothe thus constituted CSG. Note that one CSG may contain a plurality ofCSG cells. After being registered with any one of the CSG cells, theuser equipment can access the other CSG cells of the CSG to which theregistered CSG cell belongs. The Home-eNB in the LTE or the Home-NB inthe UMTS is used as the CSG cell in some cases. The user equipmentregistered with the CSG cell has a whitelist. Specifically, thewhitelist is stored in the SIM/USIM. The CSG information of the CSG cellwith which the user equipment has been registered is listed in thewhitelist. Specific examples of the CSG information include CSG-ID, TAI(Tracking Area Identity), TAC and the like. Any one of the CSG-ID andTAC is adequate as long as they are associated with each other. GCI isadequate as long as the CSG-ID, the TAC and GCI (global cell identity)are associated with each other. As can be seen from the above, the userequipment which does not have a whitelist (including a case where thewhitelist is empty in the present invention) is not allowed that makesaccess the CSG cell but is allowed that makes access only the non-CSGcell. On the other hand, the user equipment which has a whitelist isallowed that makes access the CSG cell of the CSG-ID with whichregistration has been performed as well as the non-CSG cell.

3GPP discusses that all PCI (Physical Cell Identities) are split(referred to as PCI-split) into ones reserved for CSG cells and theothers reserved for non-CSG cells (Non-Patent Document 5). Further, 3GPPdiscusses that the PCI split information is broadcast in the systeminformation from the base station to the user equipments being servedthereby. Disclosed here is the basic operation of a user equipment byPCI split. The user equipment that does not have the PCI splitinformation needs to perform cell search using all PCIs (for example,using all 504 codes). On the other hand, the user equipment that has thePCI split information is capable of performing cell search using the PCIsplit information.

Further, 3GPP has determined that the PCIs for hybrid cells are notcontained in the PCI range for CSG cells (Chapter 10.7 of Non-PatentDocument 1).

The HeNB and HNB are required to support various types of service. Forexample, an operator causes the predetermined HeNB and HNB to registeruser equipments therein and permits only the registered user equipmentsto make access the cells of the HeNB and HNB, so that the userequipments increase the available radio resource for performinghigh-speed communication. In such service, the operator correspondinglyconfigures a higher accounting fee compared with normal service. This isa service. In order to achieve the above-mentioned service, the CSG cell(Closed Subscriber Group cell) which the registered (subscribed ormember) user equipments can access is introduced. It is required toinstall a large number of CSG cells (Closed Subscriber Group cells) inshopping malls, apartment buildings, schools, companies and the like.For example, the CSG cells are required to be installed for each storein shopping malls, for each room in apartment buildings, for eachclassroom in schools, and for each section in companies in such a mannerthat only the users who have registered the respective CSG cells arepermitted to use those CSG cells. The HeNB/HNB is required not only tocomplement the communication outside the coverage of the macro cell butalso to support various types of service as described above. This leadsto a case where the HeNB/HNB is installed within the coverage of themacro cell.

As one technique studied by the LTE-A, heterogeneous networks (HetNets)are added. 3GPP handles a pico eNB (pico cell), a node for hot zonecell, an HeNB/HNB/CSG cell, a relay node, and a network node (local arearange node, a local area node, and a local node) in a local-area rangehaving a low-output power such as a remote radio head (RRH). Thus, anetwork in which such one or more local area range nodes areincorporated in a normal eNB (macro cell) is requested to be operated.The network in which one or more local area range nodes are incorporatedin the normal eNB (macro cell) is referred to as a heterogeneousnetwork, and an interference reducing method, a capacity improvingmethod and the like are studied.

In 3GPP, lower power consumption (energy saving) of an infrastructure isbeing discussed.

The following is disclosed in Non-Patent Document 8. During downlinktransmission, a base station must turn on a power supply of atransmitter power amplifier (PA). Thus, when a time for downlinktransmission is shortened, the power supply of the transmitter poweramplifier can be turned off, and lower power consumption of the basestation can be provided. Signals required in a downlink for no-active UEare a CRS, a P-SS, an S-SS and a BCH. Among the signals or channels, asignal that maximally influences a downlink transmission time is theCRS. This is because the CRSs are transmitted in all subframes. Althoughthe CRS normally has four symbols in a subframe except for the MBSFNsubframe, the CRS in the MBSFN subframe has one symbol. The MBSFNsubframe is a subframe that supports transmission using MBSFN. Thus, byusing the MBSFN subframe, a CRS transmission time can be reduced. Inthis manner, lower power consumption of the base station can beprovided.

As the MBSFN subframes, a maximum of six subframes can be configured inone radio frame (Non-Patent Document 2).

On the other hand, for lower power consumption, a new method called anextended cell DTX is proposed without using the MBSFN subframe. In theextended cell DTX, a CRS is transmitted in a first subframe (#0) pereach radio frame, and no CRS is transmitted in the other subframes. Inthe user equipment, in order to measure cell reception quality (RSRP),it is proposed that the S-SS is used instead of using the CRS.

A problem to be solved by a first embodiment is described below.

A logical architecture of an E-MBMS discussed in 3GPP is as shown inFIG. 13. The same reference numerals as those of FIG. 1 denote thecorresponding portions, which are not described. An MCE(Multi-cell/multicast Coordination Entity) 1301 is a logical element, ormay be part of another network element. The MCE controls one or morebase stations deployed under the control of the MCE. More specifically,admission control is performed and radio resources are allocated. Theradio resources are radio resources used by all the base stations in anMBSFN area for multi-cell MBMS transmission used by an MBSFN operation.The MCE determines not only allocation of the radio resource of time andfrequencies but also details of a radio configuration. The details of aradio configuration is a configuration related to, for example, amodulating scheme, a coding method or the like. The MCE executessignaling to a base station, and does not execute signaling to a userequipment.

An MBMS GW (E-MBMS Gateway) 1302 is a logical element, or may be part ofanother network element. The MBMS GW is present between a BMSC(Broadcast Multicast Service Center) 1306 and a base station.

The BMSC 1306 carries the function of user service of the MBMS. Specificexamples of the function include a security function, a synchronizationprotocol function and the like. The synchronization protocol is a methodto carry additional information that enables the base station to performradio frame transmission and a packet loss detection. The MBMS GWtransmits or broadcasts an MBMS packet to each base station thattransmits a service.

An M3 interface 1303 is defined as an interface between the MME 103 andan MCE 1301. The interface is an interface of a control plane. The M3interface 1303 is for MBMS session control signaling on an E-RAB level.The M3 interface 1303 is not used to transmit radio configuration data.

An M2 interface 1304 is defined as an interface between the MCE 1301 andan eNB 102. The interface is an interface of a control plane. The M2interface 1304 is used to transmit radio configuration data for sessioncontrol signaling to a base station in a multi-cell transmission mode.

An M1 interface 1305 is defined as an interface between the MBMS GW 1302and an eNB 102. The M1 interface 1305 is an interface of a user plane.The M1 interface 1305 is to transmit user data.

A configuring method of an MBMS subframe discussed in 3GPP is asfollows.

An MCE notifies a base station being served thereby, by using MBMSscheduling information, of an MBSFN subframe configuration. A basestation notifies a user equipment of the MBSFN subframe configuration byusing system information (SIB2) (Non-Patent Document 2 and Non-PatentDocument 9).

Thus, in the conventional technique, the MBSFN subframe configuration isnotified from the MCE to the base station, also to the user equipmentthrough the base station, and commonly used by the base stations and theuser equipments that are served by the MCE.

On the other hand, loading states of the base stations differ dependingon the base stations. That is, a low-load state (to also be referred toas low-load (Non-Patent Document 10)) or a no-load state (to also bereferred to as a no-load (Non-Patent Document 10)) in which the basestation desires to shift to an lower power consumption (energy saving)operation is a state that is independently generated in each of the basestations.

Thus, in the conventional technique, when lower power consumption of thebase stations is realized by using the MBSFN subframe, there ariseproblems that MBSFN subframe cannot be configured depending on thestates of the base stations, and an efficient energy saving operation isimpossible. Lower power consumption of the base station by using theMBSFN subframe is described below. When the base station performs lowerpower consumption, by using an MBSFN subframe in which less frequenttransmission of CRSs is performed than that of a normal subframe (asubframe except for the MBSFN subframe), a period of the power supply ofthe transmitter power amplifier is shortened.

Non-Patent Document 11 discloses that making CRS transmission lessfrequent to save a network power makes it possible to configure a largernumber of MBSFN subframes. However, more specifically, what a mainsubject of the configuration is, whether or not a larger number of MBSFNsubframes can be configured, and a concrete method of enabling a largenumber of MBSFN subframes to be configured are not disclosed.

A solution in the first embodiment is described below.

The MCE indicates a number of a subframe to be used as an MBSFN subframeto a base station. The MBSFN subframe indicated by the MCE may bereferred to as an MBSFN subframe (MCE) hereinafter. A user equipment isnotified of a number of the subframe to be used as the MBSFN subframe(MCE) through a base station.

The base station designates, in addition to the MBSFN subframe (MCE), anumber of a subframe to be used as an MBSFN subframe by the base stationitself. The MBSFN subframe additionally designated by the base stationitself may be referred to as an MBSFN subframe (eNB) hereinafter. Thenumber of subframe to be used as the MBSFN subframe (eNB) is selectedfrom subframe numbers except for the number of the subframe to be usedas the MBSFN subframe (MCE). A user equipment is notified of the numberof the subframe to be used as the MBSFN subframe (eNB) from a basestation.

As a result, the base station can use the MBSFN subframe (eNB) besidesthe MBSFN subframe (MCE). In particular, by using the MBSFN subframe(MCE) and the MBSFN subframe (eNB), a CRS can be transmitted to a userequipment. In the MBSFN subframes, the CRS is transmitted lessfrequently than normal, and transmissions of the CRS performed in theinfrastructure can be less frequent, and a power consumption of theinfrastructure can be reduced.

When the MBSFN subframe (eNB) is used in energy saving, the MBSFNsubframe (eNB) may also be referred to as a subframe for energy saving.In addition, only when the base station performs the energy savingoperation, MBSFN subframe (eNB) may be additionally designated.

For descriptive convenience, subsequently, a subframe recognized by auser equipment as a subframe using an MBSFN subframe configuration mayalso be referred to as an MBSFN subframe (UE). Two specific examples ofa method of configuring an MBSFN subframe of a base station aredisclosed below.

(1) The base station notifies the user equipment of a configuration ofan MBSFN subframe which includes the MBSFN subframe (MCE) and the MBSFNsubframe (eNB). That is, the base station notifies of an MBSFN subframe(UE) configuration. Broadcast information is used at a notification ofthe configuration. Accordingly, an effect of enabling notification ofthe MBSFN subframe configuration can be obtained to not only a userequipment that is being connected (CONNECTED) but also a user equipmentthat is idling (Idle). More specifically, SIB2 in the broadcastinformation is used. In this manner, the same configuring method as aconventional method for an MBSFN subframe is obtained, a mobilecommunication system that is good in downward compatibility can beadvantageously established.

(2) The base station notifies the user equipment of an MBSFN subframe(eNB) configuration independently of an MBSFN subframe (MCE)configuration. Independently of the MBSFN subframe configuration in SIB2of the conventional technique, the base station newly sets aconfiguration of a subframe for the MBSFN subframe (eNB) to the userequipment. Alternatively, in the MBSFN subframe configuration in theSIB2 in the conventional technique, an indicator that indicates whetheror not the configuration is for energy saving may be newly set. That is,the user equipment recognizes the subframe configured as the MBSFNsubframe (MCE) and the MBSFN subframe (eNB) as the MBSFN subframe (UE).

A specific example of a method of selecting an MBSFN subframe (eNB) ofthe base station is disclosed below.

The base station configures a subframe different from the MBSFN subframe(MCE) as the MBSFN subframe (eNB). The base station may transmit MBMSdata by a resource except for the CRS in the MBSFN subframe (MCE). Thus,even though the MBSFN subframe (MCE) is used for energy saving, in theresource except for the CRS, the base station must turn on the powersupply of the transmitter power amplifier, and a less energy savingeffect is obtained. Thus, by using this method, a subframe differentfrom the MBSFN subframe (MCE) is configured as a subframe for energysaving to make it possible to establish a mobile communication systemhaving a great effect for lower power consumption.

A specific operation example using the first embodiment is describedwith reference to FIG. 14.

In this operation example, a case where the specific example (2) is usedin a method of configuring an MBSFN subframe of a base station isdisclosed. A case where the specific example (2) is used in a method ofselecting an MBSFN subframe (eNB) of a base station is disclosed.

In Step ST1401, the MCE notifies a base station (eNB1) being servedthereby of the MBSFN subframe (MCE).

In Step ST1402, the MCE notifies a base station (eNB2) being servedthereby of the MBSFN subframe (MCE). The MCE notifies all the basestations that perform the same MBMS transmission and are served therebyof the same MBSFN subframe (MCE). It is to support the MBSFNtransmission. In this operation example, for example, it is assumed thata second subframe (#1) and a third subframe (#2) are configured as MBSFNsubframes (MCE).

In Step ST1403, the base station (eNB1) judges whether or not toconfigure the MBSFN subframe (eNB). In the case of judging that theMBSFN subframe is configured, the flow shifts to Step ST1404. In thecase of judging that the MBSFN subframe is not configured, the judgmentin Step ST1403 is repeated. When the MBSFN subframe is used in an energysaving operation, in Step ST1403, it may be judged whether or not theenergy saving operation is executed. In this case, when it is judgedthat the energy saving operation is executed, the flow shifts to StepST1404. When it is judged that the energy saving operation is notexecuted, the judgment in Step ST1403 is repeated.

In Step ST1404, the base station (eNB1) selects the MBSFN subframe(eNB). In this operation example, a subframe different from #1 and #2serving as the MBSFN subframes (MCE) is selected as the MBSFN subframe(eNB). In this operation example, for example, it is assumed that aseventh subframe (#6) and an eighth subframe (#7) are configured asMBSFN subframes (eNB).

In Step ST1405, the base station (eNB1) notifies a user equipment beingserved thereby of an MBSFN subframe (MCE) configuration. In thisoperation example, #1 and #2 are notified as subframes reserved for theMBSFN in a downlink.

In Step ST1406, the base station (eNB1) notifies a user equipment beingserved thereby of an MBSFN subframe (eNB) configuration. In thisoperation example, #6 and #7 are notified as subframes reserved for theMBSFN in a downlink.

In Step ST1407, the user equipment operates using the MBSFN subframe(MCE) received in Step ST1405 and the MBSFN subframe (eNB) received inStep ST1406 as subframes reserved for the MBSFN in a downlink. In thisoperation example, the user equipment operates using #1, #2, #6 and #7as subframes reserved for the MBSFN in a downlink. The MBSFN frameconfiguration is the same as that in the conceptual diagram shown inFIG. 3.

The first embodiment can achieve the effects below.

Other than the configuration notified by the MCE to the base station,the base station can configure the MBSFN subframe by itself for a userequipment being served thereby. In this manner, the MBSFN subframe canbe configured according to operation states which differ depending onbase stations, and frequency of transmitting a CRS can be adjusted. Anefficient energy saving operation that is suitable for each base stationcan be performed. The above operations can contribute to lower powerconsumption on the network side.

Although, in the above description, “the number of a subframe to be usedas the MBSFN subframe (eNB) is selected from subframe numbers except forthe number of a subframe to be used as the MBSFN subframe (MCE)”.However, “the number of a subframe to be used as the MBSFN subframe(eNB) may be selected to be completely equal to the number of the MBSFNsubframe (MCE) or to partially overlap the number of the MBSFN subframe(MCE)”.

In this case, a specific example of a method of configuring an MBSFNsubframe of a base station may be as follows. When the number of thesubframe to be used as the MBSFN subframe (MCE) is completely equal tothe number of the subframe to be used as the MBSFN subframe (eNB), (1)the base station notifies a user equipment of the MBSFN subframe (MCE)configuration. (2) The base station notifies the user equipment of anMBSFN subframe (eNB) configuration.

In this case, the following portion may be referred to as a subframe forenergy saving. (1) An MBSFN subframe (eNB) including an overlappingportion between a number of a subframe to be used as the MBSFN subframe(eNB) and a number of the MBSFN subframe (MCE) may be referred to as asubframe for energy saving. (2) Among the subframes configured as theMBSFN subframe (eNB), a subframe that does not overlap the number of theMBSFN subframe (MCE) may be referred to as a subframe for energy saving.

Also, the MBSFN subframe (MCE) may be included in the subframes forenergy saving or configured as a subframe for energy saving. In thiscase, even when the base station receives MBMS data (control data anduser data) to perform transmission in the MBSFN subframe (MCE), the basestation may perform an energy saving operation. The base station mayturn off transmission at a transmission timing except for the timing ofthe CRS in a subframe configured as the subframe for energy saving. Evenwhen the base station receives MBMS data from the MBMS GW, the BMSC orthe MCE to transmit a subframe for energy saving, the power supply ofthe transmitter power amplifier may be turned off in a radio resourcefor transmitting the MBMS data. In this manner, even though the basestation cannot configure the MBSFN subframe for a user equipment beingserved thereby by itself, energy saving using the MBSFN subframe can beperformed according to operation states which differ depending on basestations.

In addition, information representing whether or not the MBSFN subframe(MCE) can be used for energy saving may be configured, and the MCE maynotify a base station of the information. On the basis of theinformation, the MBSFN subframes used for energy saving may bedetermined.

The case where the MBSFN subframe (eNB) is configured when the basestation is in an energy saving operation state has been described above.However, the present invention is not limited to the case, and an MBSFNsubframe (eNB) is configured depending on an operation state of a basestation to make it possible to reduce a power consumption.

The case where the MBSFN subframe having a CRS transmission performedless frequent than that of a normal subframe having a CRS transmissionperformed frequently has been described. However, the present inventionis not limited to the case, by using a radio resource having a CRStransmission performed less frequently than normal, it becomes possibleto reduce a power consumption.

First Modification of First Embodiment

In a case where the first embodiment is used, the following problemoccurs.

In the conventional technique, neighbor cell information includesinformation representing whether or not the MBSFN is supported(Non-Patent Document 2). The information is referred to as a neighborcell configuration (Neigh Cell Config), and is included in the SIB3 andSIB5 of broadcast information or a measurement object. The informationis expressed by two bits. The meanings of combinations of the bits areas follows. A combination “00” represents that the same MBSFN subframeconfiguration as that in a serving cell is not present in all theneighbor cells. In other words, the neighbor cells include a cell havingan MBSFN subframe configuration different from that of a serving cell. Acombination “10” represents that each of all the neighbor cells has thesame MBSFN subframe configuration as that of a serving cell or the MBSFNsubframe configuration included in the MBSFN subframe configuration ofthe serving cell. A combination “01” represents that the MBSFN subframeis not configured in each of all the neighbor cells. A combination “11”represents that uplink allocation or downlink allocation different fromthat in the serving cell is present in the neighbor cell in a TDD (TimeDivision Duplex) system.

When the base station can configure a subframe except for the MBSFNsubframe (MCE) as the MBSFN subframe (eNB) by using the firstembodiment, the MBSFN subframe actually used by the base station may bemismatched with information that is notified as neighbor cellinformation by the neighbor cell of the base station to a user equipmentbeing served thereby.

In the conventional technique, the user equipment measures receptionquality (RSRP) of a cell by using the CRS. The CRS resources of theMBSFN subframes are different from the CRS resources of a subframeexcept for the MBSFN subframe.

Thus, when the MBSFN subframe actually used by the base station ismismatched with the information that notified as neighbor cellinformation by a neighbor cell of the base station to the userequipment, an error occurs in a measurement result of the neighbor cellobtained by the user equipment. This is because the user equipment maymeasure an RSRP as a CRS for a symbol for which the CRS is not actuallytransmitted. Furthermore, this is because the user equipment may notperform RSRP measurement to the CRS for a symbol for which the CRS isactually transmitted. Due to the error of the measurement result, theuser equipment may hand over a cell different from an original best cellor may reselect a cell. In this manner, effective utilization of a radioresource cannot be provided, or a uselessly high uplink transmissionpower is used to disadvantageously increase uplink interference.

A specific example that causes problems is described with reference toFIG. 15. The same reference numerals as those of FIGS. 1 and 13 denotethe corresponding portions, which are not described.

Location is described first. There are an eNB1 (102-1), an eNB2 (102-2)and eNB3 (102-3) that are served by the MCE 1301. The MCE 1301 and theeNB1 (102-1) are connected by an M2 interface 1304-1, the MCE 1301 andthe eNB2 (102-2) are connected by an M2 interface 1304-2, and the MCE1301 and the eNB3 (102-3) are connected by an M2 interface 1304-3. Thereis a user equipment 1 (101-1) being served by the eNB1 (102-1), there isa user equipment 2 (101-2) being served by the eNB2 (102-2), and thereis a user equipment 3 (101-3) being served by the eNB3 (102-3). It isassumed that there are the eNB2 (101-2) and the eNB3 (101-3) as neighborcells of the eNB1 (101-1). It is assumed that there are the eNB1 (101-1)and the eNB3 (101-3) as neighbor cells of the eNB2 (101-2). It isassumed that there are the eNB1 (101-1) and the eNB2 (101-2) as neighborcells of the eNB3 (101-3).

A specific example that causes problems is described with reference toFIGS. 14 and 15. It is assumed that the eNB3 (101-3) in FIG. 15 isomitted in FIG. 14. The MCE 1301 notifies the eNB1 (102-1), the eNB2(102-2) and the eNB3 (102-3) serving as base stations being servedthereby of the MBSFN subframe (MCE) (corresponding to Step ST1401 andStep ST1402 in FIG. 14). For example, it is assumed that a secondsubframe (#1) and a third subframe (#2) are configured as MBSFNsubframes (MCE). It is assumed that the eNB1 (102-1) executes an energysaving operation to configure the MBSFN subframe (eNB) (corresponding toStep ST1404 in FIG. 14). In this case, a subframe different from #1 and#2 serving as the MBSFN subframes (MCE) are configured as the MBSFNsubframe (eNB). For example, it is assumed that a seventh subframe (#6)and an eighth subframe (#7) are configured as MBSFN subframes (eNB).

On the other hand, the eNB2 (102-2) having the eNB1 (102-1) as aneighbor cell has no way of knowing the MBSFN subframe (eNB) of the eNB1(102-1). Thus, the eNB2 (102-2) may notify the user equipment 2 (101-2)being served thereby of signaling bits “10” as information (a type ofneighbor cell information) representing whether or not the MBSFN issupported. The signaling bits “10” represents that each of all theneighbor cells (eNB1 and eNB3) has the same MBSFN subframe configurationas that of own cell (eNB2) or the MBSFN subframe configuration includedin the MBSFN subframe configuration of own cell. The user equipment 2(101-2) that receives the information (a type of neighbor cellinformation) representing whether or not the MBSFN is supported measuresa reference symbol received power (RSRP) on the assumption that the eNB1(101-1) and the eNB3 (101-3) have, as neighbor cells, the same MBSFNsubframe configuration as that of a serving cell or an MBSFN subframeconfiguration included in the MBSFN subframe configuration of theserving cell. More specifically, the user equipment 2 measures RSRPs for#1 and #2 serving as the MBSFN subframes (MCE) notified from the MCE byusing one symbol of CRS, and measures an RSRP for a subframe except forthe MBSFN subframe (MCE) by using, for example, four symbols of CRS. Onthe other hand, the eNB1 (101-1) performs an operation for #1, #2, #6and #7 by using the MBSFN subframe configuration. That is, the eNB1(101-1) transmits one symbol of CRS for #1, #2, #6 and #7, and transmitsfour symbols of CRS to other subframes.

As described above, the following error occurs in measurement of theeNB1 in neighbor cell measurement performed by the user equipment 2.With respect to the subframes #6 and #7, the user equipment 2 includesthree symbols for which the eNB1 does not actually transmit a CRS inmeasurement objects of the RSRP. Thus, the RSRP value of the eNB1 in theuser equipment 2 may be lower than a real value. In this manner, even ina circumstance in which the best cell is the eNB1 for the user equipment2, a cell other than the eNB1 may be reselected or handed over. In thismanner, effective utilization of a radio resource cannot be provided, ora uselessly high uplink transmission power is used to disadvantageouslyincrease uplink interference.

A solution in the first modification of the first embodiment isdescribed below. Parts different from the solution of the firstembodiment are mainly described below. Undescribed parts are the same asthose in the first embodiment.

The base station notifies neighbor cells of an MBSFN subframeconfiguration of own cell. Neighbor cell information is updated on thebasis of the information and the updated information is notified to theuser equipment being served by the base station the configurationnotified. The user equipment executes neighbor cell measurement by usingthe neighbor cell information.

Notification to neighbor cells may be executed only when the MBSFNsubframe (eNB) is configured. The notification may be performed onlywhen a subframe different from the MBSFN subframe (MCE) is configured asthe MBSFN subframe (eNB).

Six specific examples of the MBSFN subframe configuration of which theneighbor cells are notified are disclosed below. (1) An MBSFN subframe(UE) obtained when the specific example (1) of a method of configuringan MBSFN subframe of a base station is used in the first embodiment. (2)An MBSFN subframe (eNB) obtained when the specific example (2) of amethod of configuring an MBSFN subframe of a base station is used in thefirst embodiment. The MBSFN subframe (MCE) may also be notified. (3)Among the MBSFN subframes (eNB), a subframe different from the MBSFNsubframe (MCE). (4) information representing whether or not the MBSFNsubframe is configured independently of a notification of the MCE. Thatis, information representing whether or not a subframe different fromthat of a notification of the MCE is configured as the MBSFN subframe(eNB). (5) Information representing that the MBSFN subframe isconfigured independently of a notification of the MCE. That is,information representing that the MBSFN subframe (eNB) is configuredindependently of a notification of the MCE. (6) Information representingthat the MBSFN subframe is not configured independently of anotification of the MCE. That is, information representing that asubframe different from that of a notification of the MCE is notconfigured as the MBSFN subframe (eNB).

Three specific examples of an interface used for notification to theneighbor cells are disclosed below. (1) The base station performsnotification to the neighbor cells by using the X2 interface. (2) Thebase station performs notification to the MME by using the S1 interface.The MME performs notification to the neighbor cells of the base stationby using the S1 interface. (3) The base station performs notification tothe MCE by using the M2 interface. The MCE performs notification to theMME by using the M3 interface. The MME performs notification to theneighbor cells of the base station by using the S1 interface.

Five specific examples of a method of selecting a neighbor cell aredisclosed below. (1) A determination is made based on a measurementresult of a neighbor radio environment of the base station. As aspecific example of the neighbor radio environment, a measurement resultof a neighbor cell is given. As specific examples of a measurementresult of a neighbor cell, reception quality, a received power, a pathloss and the like are given. When, in the measurement result of theneighbor radio environment, reception quality or a received power of acertain base station is a certain threshold value or more (or largerthan the threshold value), the base station selects the certain basestation as neighbor cell that performs notification of the MBSFNsubframe configuration of own cell. When, in the measurement result ofthe neighbor radio environment, a path loss of a certain base station issmaller than a certain threshold value (or equal to the threshold valueor less), the base station selects the certain base station as neighborcell that performs notification of the MBSFN subframe configuration ofown cell. (2) A judgment is made by a measurement report from a userequipment being served by the base station. For example, according tothe measurement report, a cell reported to be good in reception qualityby own cell is selected as a neighbor cell that performs notification ofthe MBSFN subframe configuration of own cell. The good reception qualityincludes, for example, a case where a received power is higher than thatof own cell, a case where a path loss is smaller than that of own cell,and the like. (3) A cell that has been selected by a handover target (tobe also referred to as a target cell) is selected as a neighbor cellthat performs notification of the MBSFN subframe configuration of owncell. (4) A cell that has been selected by a cell reselect target isselected as a neighbor cell that performs notification of the MBSFNsubframe configuration of own cell. (5) A base station including thecorresponding base station in a neighbor cell is selected.

Two specific examples of a main body that updates neighbor cellinformation are disclosed below. (1) The base station that receives thenotification updates the neighbor cell information. This example has ahigh affinity to the specific example (1) of the interface used fornotification to the neighbor cell. This is because the notification isdirectly given to the base station without through the MME. (2) The MMEthat receives the notification updates neighbor cell information of abase station having the base station that transmits the notification asa neighbor cell. This example has a high affinity to the specificexamples (2) and (3) of the interface used for notification to theneighbor cell. This is because the notification is performed through theMME.

A specific operation example using the first modification of the firstembodiment is described with reference to FIG. 16. The same referencenumerals as those of FIG. 14 denote the corresponding portions, whichare not described. Location is the same as the location described withreference to FIG. 15, which are not described.

In this operation example, a case where the specific example (3) is usedin the MBSFN subframe configuration of which neighbor cells are notifiedis disclosed. A case where the specific example (2) is used in aninterface used in notification to the neighbor cells are disclosedbelow. A case where a specific example (5) is used in the method ofselecting a neighbor cell is disclosed below. A case where the specificexample (2) is used in a main body that updates neighbor cellinformation is disclosed below.

In Step ST1601, the base station (eNB1) notifies the MME of a subframedifferent from the MBSFN subframe (MCE) of the MBSFN subframes (eNB) asinformation of the MBSFN subframe configuration. In this operationexample, the MBSFN subframe (MCE) are #1 and #2. The MBSFN subframes(eNB) are #6 and #7. Thus, pieces of information of which the basestation (eNB1) notifies the MME become #6 and #7. The S1 interface isused for the notification.

In Step ST1602, the MME selects a neighbor cell that performsnotification of the MBSFN subframe configuration of the base station(eNB1). A base station including the base station (eNB1) in a neighborcell is selected. In this operation example, the eNB1 (101-1) and theeNB3 (101-3) are present as neighbor cells of the eNB2 (101-2), and theeNB1 (101-1) and the eNB2 (101-2) are present as neighbor cells of theeNB3 (101-3). Thus, in Step ST1602, the MME selects the eNB2 (101-2) andthe eNB3 (101-3). Subsequently, the eNB3 (101-3) is considered to beequal to the eNB2 (101-2), which is not described.

In Step ST1603, the MME updates the neighbor cell information of thebase station selected in Step ST1602. Information representing whetheror not the MBSFN serving as the neighbor cell information is supportedis updated. The MME may perform determination based on the informationreceived in Step ST1601. In Step ST1601, the MME can judge that the eNB1configures a subframe different from the MBSFN subframe (MCE) as theMBSFN subframe configuration. In this operation example, the MBSFNsubframe configuration of the eNB2 (101-2) is the MBSFN subframe (MCE)received in Step ST1401. Thus, the subframes become #1 and #2. Thus, theinformation (neighbor cell information of the eNB2) representing whetheror not the MBSFN is supported is changed (updated) by the MME intoinformation representing that the same MBSFN subframe configuration asthat of the serving cell (eNB2) is not included in all the neighborcells. If a conventional technique is used as the neighbor cellinformation, the information is changed (updated) into signaling bits“00”.

In Step ST1604, the MME notifies the base station selected in StepST1602 of the neighbor cell information updated in Step ST1603. The S1interface may be used for the notification.

In Step ST1605, the eNB2 (103-2) that receives the updated neighbor cellinformation notifies the user equipment 2 being served thereby of theupdated neighbor cell information.

In Step ST1607, the user equipment 2 that receives the updated neighborcell information performs neighbor cell measurement by using the updatedneighbor cell information. As a specific example, the user equipment 2performs the neighbor cell measurement on the assumption that a basestation that performs an MBSFN subframe configuration different fromthat of the serving cell (eNB2) is included in the neighbor cells.

The first modification of the first embodiment can achieve the effectsbelow in addition to those of the first embodiment. In addition to theconfiguration notified by the MCE to the base station, even when thebase station can configure the MBSFN subframe for a user equipment beingserved thereby by itself, neighbor cell information notified from theneighbor cell of the base station can be updated. Thus, in a userequipment being served by a neighbor cell of the base station thatconfigures the MBSFN subframe by itself, in neighbor cell measurementthat targets the base station that configures the MBSFN subframe byitself, an RSRP measurement error caused by configuring the MBSFNsubframe by itself does not occur. In this manner, the user equipmentcan be prevented from being handed over to or reselecting a celldifferent from the original best cell. Thus, a useless radio resourcecan be prevented from occurring, and a uselessly high uplinktransmission power can be prevented from being used.

Second Modification of First Embodiment

In a case where the first embodiment is used, a new problem occurs asfollows.

Since data that must be transmitted per unit time and is related to anMBMS increases, it is discussed that the MCE changes configurations toincrease the MBSFN subframe (MCE).

By increasing MBMS data, configurations are changed to increase theMBSFN subframe (MCE) configured in the MCE. Accordingly, if any deviceis not used, MBSFN subframe configuration that is notified from the basestation being served by the MCE to the user equipment being served bythe base station must be changed. In this manner, a change of systeminformation occurs. Thus, the base station notifies the user equipmentof a system information change (systemInfoModification) by paging(Non-Patent Document 2). The user equipment that receives the systeminformation change by paging must receive the updated system informationeven though the user equipment is being in, for example, an idle state(Non-Patent Document 2). Lower power consumption is provided such thatthe user equipment being in an idle state performs intermittentreception. By interrupting the intermittent reception for receivingsystem information, an increase in power consumption of the userequipment occurs.

A specific example that causes problems is described with reference toFIG. 17. The same reference numerals as those of FIG. 14 denote thecorresponding portions, which are not described.

In this specific example, as a method of configuring an MBSFN subframeof a base station in the first embodiment, an MBSFN subframe includingthe MBSFN subframe (MCE) and the MBSFN subframe (eNB) are configured forthe user equipment. That is, a case where the base station employs thespecific example (1) that configures the MBSFN subframe (UE) isdescribed below.

In Step ST1701, the base station (eNB1) notifies the user equipmentbeing served thereby of the MBSFN subframe (MCE) received in Step ST1402and the MBSFN subframe (UE) including the MBSFN subframe (eNB) selectedin Step ST1404. In this specific example, #1, #2, #6 and #7 are notifiedas subframes reserved for the MBSFN in a downlink.

In Step ST1702, the user equipment operates using the MBSFN subframe(UE) received in Step ST1701 as a subframe reserved for the MBSFN in adownlink. In this specific example, the user equipment operates using#1, #2, #6 and #7 as subframes reserved for the MBSFN in a downlink. TheMBSFN frame is configured like the MBSFN frame in the conceptual diagramshown in FIG. 3.

In Step ST1703, the MCE judges whether or not the configuration of theMBSFN subframe (MCE) must be changed. When the change is required, theflow shifts to Step ST1704. When the change is not required, thejudgment in Step ST1703 is repeated. In addition to this, it may bejudged whether or not the MBSFN subframe (MCE) must be increased. Inthis case, when the increase is required, the flow shifts to StepST1704. When the increase is not required, the judgment in Step ST1703is repeated.

In Step ST1704, the MCE updates the MBSFN subframe (MCE). In thisspecific example, it is assumed that #1, #2 and #8 are selected as theMBSFN subframes (MCE). More specifically, it is assumed that #8 is addedas the MBSFN subframe (MCE).

In Step ST1705, the MCE notifies the base station (eNB2) being servedthereby of the updated MBSFN subframe (MCE) updated in Step ST1704.

In Step ST1706, the MCE notifies the base station (eNB1) being servedthereby of the updated MBSFN subframe (MCE) updated in Step ST1704.Subsequently, the eNB2 is considered to be equal to the eNB1, which isnot described.

In Step ST1707, the base station (eNB1) judges whether or not the MBSFNsubframe (UE) must be updated. When the updating is required, the flowshifts to Step ST1708. When the updating is not required, the judgmentin Step ST1707 is repeated. In this specific example, subframes that arenotified to the user equipment being served by the base station in StepST1701 and are reserved for the MBSFN in a downlink are #1, #2, #6 and#7. On the other hand, in Step ST1706, #1, #2 and #8 are received as theMBSFN subframe (MCE) by the MCE. Thus, as the MBSFN subframe (MCE) andthe MBSFN subframe (UE) including the MBSFN subframe (eNB) selected inStep ST1404, #1, #2, #6, #7 and “#8” are given. Thus, in this specificexample, in Step ST1707, the base station (eNB1) judges that the MBSFNsubframe (UE) must be updated.

In Step ST1708, the base station (eNB1), by using paging for the userequipment being served thereby, performs system information changenotification to the user equipment being served thereby.

In Step ST1709, the user equipment judges whether or not the systeminformation change notification is received. When the system informationchange notification is received, the flow shifts to Step ST1711. Whenthe system information change notification is not received, the judgmentin Step ST1709 is repeated. In this specific example, since the systeminformation change notification is performed in Step ST1708, it isjudged in Step ST1709 that the system information change notification isreceived, the flow shifts to Step ST1711.

In Step ST1710, the base station (eNB1) notifies the user equipmentbeing served thereby of the MBSFN subframe (MCE) received in Step ST1706and the MBSFN subframe (UE) including the MBSFN subframe (eNB) selectedin Step ST1404. In this specific example, #1, #2, #6, #7 and “#8” arenotified as subframes reserved for the MBSFN in a downlink.

The user equipment in Step ST1711 receives system information. Thisreception is executed even though the user equipment is being in, forexample, an idle state.

As described above, if any device is not used, a system informationchange of the base station is performed each time an amount of data ofMBMS varies, and intermittent reception performed by the user equipmentto receive the updated system information is interrupted. In thismanner, an increase in power consumption of the user equipment occurs.

A solution in the second modification of the first embodiment isdescribed below. Parts different from the solution of the firstembodiment are mainly described below. Undescribed parts are the same asthose in the first embodiment.

The base station notifies the MCE of an MBSFN subframe configuration ofown cell. When the MCE updates the MBSFN subframe configuration, the MCEperforms adjustment by using the information.

Notification to the MCE may be executed only when the MBSFN subframe(eNB) is configured. The notification may be performed only when asubframe different from the MBSFN subframe (MCE) is configured as theMBSFN subframe (eNB).

Three specific examples of the MBSFN subframe configuration of which theMCE notifies are disclosed below. (1) An MBSFN subframe (UE) obtainedwhen the specific example (1) of a method of configuring an MBSFNsubframe of a base station is used in the first embodiment. (2) An MBSFNsubframe (eNB) obtained when the specific example (2) of a method ofconfiguring an MBSFN subframe of a base station is used in the firstembodiment. The MBSFN subframe (MCE) may also be notified. (3) Among theMBSFN subframes (eNB), a subframe different from the MBSFN subframe(MCE).

Two specific examples of adjustment performed by the MCE are disclosedbelow. (1) When the MCE increases the MBSFN subframe (MCE), it is judgedwhether or not, in the MBSFN subframe configuration of the base stationthat receives notification from the base station, a subframe except fora subframe currently used as the MBSFN subframe (MCE) is present. Whenthe subframe is present, the subframe is selected as an MBSFN subframe(MCE) that increases the subframe. (2) When the MCE reduces the MBSFNsubframe (MCE), it is judged whether or not, in the MBSFN subframe (eNB)that receives notification from the base station, a subframe currentlyused as the MBSFN subframe (MCE) is present. When the subframe ispresent, the subframe is selected as an MBSFN subframe (MCE) thatreduces the subframe. The adjustment may be similarly performed betweena plurality of base stations being served by the MCE.

Three specific examples of a notification timing from the base stationto the MCE are disclosed below. (1) Notification is periodicallyperformed. (2) When the MBSFN subframe configuration in the base stationis changed, the notification is performed. Alternatively, when the MBSFNsubframe (eNB) is changed, the notification is performed.

As an example of an interface used for notification from the basestation to the MCE, an M2 interface between the base station and the MCEis given. (3) When an MBSFN subframe (eNB) notification request isreceived from the MCE, the notification is performed. In order torecognize a specific subframe that is configured by the base stationbeing served by the MCE as the MBSFN subframe (eNB), the MCE may notifythe base station of the MBSFN subframe (eNB) notification request priorto the change of the MBSFN subframe (MCE). The base station thatreceives the MBSFN subframe (eNB) notification request from the MCEnotifies the MCE of the MBSFN subframe (eNB).

A specific operation example using the second modification of the firstembodiment is described with reference to FIG. 18. The same referencenumerals as those of FIG. 14 and FIG. 17 denote the correspondingportions, which are not described.

In this operation example, a case where the specific example (2) is usedin the MBSFN subframe configuration of which the MCE is notified isdisclosed. A case where the base station (2) is used at a notificationtiming from the base station to the MCE is disclosed below.

In Step ST1801, the base station (eNB1) notifies the MCE of the MBSFNsubframe (eNB) as information of the MBSFN subframe configuration. Inthis operation example, the MBSFN subframe (MCE) notified in Step ST1401and Step ST1402 are defined as #1 and #2. The MBSFN subframes (eNB)selected in Step ST1404 are defined as #2, #6 and #7. Thus, pieces ofinformation given from the base station (eNB1) to the MCE in Step ST1801are #2, #6 and #7. The notification uses the M2 interface.

In Step ST1802, the MCE judges whether or not the MBSFN subframe (MCE)must be added. When the addition is required, the flow shifts to StepST1803. When the addition is not required, the flow shifts to StepST1805.

Subsequently, a case where the MCE increases the MBSFN subframe (MCE) isdescribed first. More specifically, in Step ST1802, since the MCE judgesthat the MBSFN subframe (MCE) must be added, the flow shifts to StepST1803.

In Step ST1803, the MCE judges whether or not, in the MBSFN subframe(eNB) of a base station that receives the notification from the basestation, a subframe except for the subframe currently used as the MBSFNsubframe (MCE) is present. When the subframe is present, the flow shiftsto Step ST1804. When the subframe is not present, the flow shifts toStep ST1704. In Step ST1704, the MCE updates the MBSFN subframe (MCE).In this operation example, as subframes except for the subframecurrently used as the MBSFN subframe (MCE) in the MBSFN subframe (eNB),#6 and #7 are present. Thus, in Step ST1803, it is judged that thesubframe is present, and the flow shifts to Step ST1804.

In Step ST1804, the MCE selects, as a subframe added to the MBSFNsubframe (MCE), a subframe except for the subframe currently used as theMBSFN subframe (MCE) in the MBSFN subframe (eNB). In this operationexample, it is assumed that #6 is selected.

Even though the MBSFN subframe (MCE) is updated by performing theprocess, the MBSFN subframe (UE) need not be updated in the base station(eNB1). Thus, in Step ST1707, it is judged that the MBSFN subframe (UE)need not be updated. In this manner, a system information change doesnot occur.

In Step ST1706, the MCE notifies the base station (eNB1) being servedthereby of the updated MBSFN subframe (MCE) updated in Step ST1704 or inStep ST1804. In this operation example, as the MBSFN subframes (MCE),notification of #1, #2 and #6 is performed.

In Step ST1707, the base station (eNB1) judges whether or not the MBSFNsubframe (UE) must be updated. In this operation example, subframes thatare notified to the user equipment being served by the base station inStep ST1701 and are reserved for the MBSFN in a downlink are #1, #2, #6and #7. On the other hand, in Step ST1706, #1, #2 and #6 are received asthe MBSFN subframe (MCE) by the MCE. Thus, as the MBSFN subframe (MCE)and the MBSFN subframe (UE) including the MBSFN subframe (eNB) (#2, #6and #7) selected in Step ST1404, #1, #2, #6 and #7 are given. Thus, itis judged that the MBSFN subframe (UE) need not be updated. In thismanner, a system information change does not occur, and shift to StepST1708 does not occur.

A case where the MCE reduces the MBSFN subframe (MCE) is describedbelow. More specifically, in Step ST1802, since the MCE judges that theMBSFN subframe (MCE) need not be added, the flow shifts to Step ST1805.

In Step ST1805, the MCE judges whether or not, in the MBSFN subframe(eNB) of a base station that receives the notification from the basestation, a subframe currently used as the MBSFN subframe (MCE) ispresent. When the subframe is present, the flow shifts to Step ST1806.When the subframe is not present, the flow shifts to Step ST1704. InStep ST1704, the MCE updates the MBSFN subframe (MCE). In this operationexample, as a subframe currently used as the MBSFN subframe (MCE) in theMBSFN subframe (eNB), #2 is present. Thus, in Step ST1805, it is judgedthat the subframe is present, and the flow shifts to Step ST1806.

In Step ST1806, the MCE selects, as a subframe deleted from the MBSFNsubframe (MCE), a subframe currently used as the MBSFN subframe (MCE) inthe MBSFN subframe (eNB). In this operation example, it is assumed that#2 is selected. Even though the MBSFN subframe (MCE) is updated byperforming the process, the MBSFN subframe (UE) need not be updated inthe base station (eNB1). Thus, in Step ST1707, it is judged that theMBSFN subframe (UE) need not be updated. In this manner, a systeminformation change does not occur.

In Step ST1706, the MCE notifies the base station (eNB1) being servedthereby of the updated MBSFN subframe (MCE) updated in Step ST1704 or inStep ST1806. In this operation example, as the MBSFN subframes (MCE),notification of #1 and #6 is performed.

In Step ST1707, the base station (eNB1) judges whether or not the MBSFNsubframe (UE) must be updated. In this operation example, subframes thatare notified to the user equipment being served by the base station inStep ST1701 and are reserved for the MBSFN in a downlink are #1, #2, #6and #7. On the other hand, in Step ST1706, #1 and #6 are received as theMBSFN subframe (MCE) by the MCE. Thus, as the MBSFN subframe (MCE) andthe MBSFN subframe (UE) including the MBSFN subframe (eNB) (#2, #6 and#7) selected in Step ST1404, #1, #2, #6 and #7 are given. Thus, it isjudged that the MBSFN subframe (UE) need not be updated. In this manner,a system information change does not occur, and shift to Step ST1708does not occur.

Note that the number of MBSFN subframes to be updated is not limited toone and may be two or more.

In the modification, an example obtained by combining the firstembodiment to the modification is mainly described. However, acombination between the first modification of the first embodiment andthe modification can be used.

The second modification of the first embodiment can achieve the effectsbelow in addition to those of the first embodiment.

Even when addition of the MBSFN subframe (MCE) is required by increasingdata of the MBMS, the MCE performs adjustment to make it possible tominimize a change of definition (MBSFN subframe Configuration) of asubframe reserved for the MBSFN using broadcast information from a basestation being served by the MCE to a user equipment. In this manner, achange of system information can be suppressed. Thus, reception of thesystem information with discontinuous reception interruption of the userequipment can be suppressed. In this manner, an increase in powerconsumption of the user equipment can be prevented.

Third Modification of First Embodiment

In a case where the second modification of the first embodiment is used,the following problem occurs.

The MBSFN subframe configuration notified from the base station to theMCE may not include a subframe except for the subframe currently used inthe MBSFN subframe (MCE). In this case, adjustment cannot be performedby the MCE disclosed in the second modification of the first embodiment,and a problem of the second modification of the first embodiment occursagain.

When the MBSFN subframe (eNB) is configured for each base stations, anda plurality of base stations are served by the MCE, the problem moredominantly appears. This is because, when a large number of MBSFNsubframe configurations notified from a large number of base stationsbeing served by the MCE to the MCE do not include a subframe except fora subframe currently used as the MBSFN subframe (MCE), the effects ofadjustment obtained by the MCE disclosed in the second modification ofthe first embodiment do not influence all the base stations.

A solution in the third modification of the first embodiment isdescribed below. Parts different from the solution of the firstembodiment are mainly described below. Undescribed parts are the same asthose in the first embodiment.

The MCE notifies a base station being served thereby of information of apriority order of a subframe configured as the MBSFN subframe (MCE).When the base station that receives the information executes or changesa configuration of the MBSFN subframe (eNB), adjustment is performed byusing the information of the priority order. The adjustment may becommonly performed by a plurality of base stations being served by theMCE.

In the conventional technique, a maximum of six MBSFN subframes can beconfigured in one radio frame. Subframes that can be configured as MBSFNsubframes are a second subframe (#1), a third subframe (#2), a fourthsubframe (#3), a seventh subframe (#6), an eighth subframe (#7) and aninth subframe (#8) (Non-Patent Document 2). A specific example ofinformation of a priority order when the third modification of the firstembodiment in the conventional technique is shown in FIG. 19.

FIG. 19 shows a correspondence between a subframe configured as theMBSFN subframe (MCE) and a priority order. As the MBSFN subframe (MCE),a subframe configured to have the first priority order is the secondsubframe (#1). As the MBSFN subframe (MCE), a subframe set to have thesecond priority order is the third subframe (#2). As the MBSFN subframe(MCE), a subframe set to have the third priority order is the seventhsubframe (#6). As the MBSFN subframe (MCE), a subframe set to have thefourth priority order is the eighth subframe (#7). As the MBSFN subframe(MCE), a subframe set to have the fifth priority order is the fourthsubframe (#3). As the MBSFN subframe (MCE), a subframe set to have thesixth priority order is the ninth subframe (#8). A plurality ofsubframes may have the same priority order.

The priority order may be statically determined or may besemi-statically determined on the network side. For example, twonotifying methods to a base station being served by the MCE when thepriority order is semi-statically determined in the MCE are disclosedbelow. (1) The MCE performs notification to the base station beingserved thereby by using the M2 interface. (2) The MCE notifies the MMEof the priority order by using an M3 interface, and the MME notifies thebase station of the priority order by using the S1 interface.

Two specific examples of adjustment performed by the base station aredisclosed below. (1) When the base station increases the MBSFN subframe(eNB), in a subframe except for a subframe currently used in the MBSFNsubframe (eNB), a subframe having the highest priority order receivedfrom the MCE is preferentially configured. When the base station is freefrom a load, or when the base station is in a low-loading state, theMBSFN subframe (eNB) may be increased. (2) When the base station reducesthe MBSFN subframe (eNB), in the subframe currently used as the MBSFNsubframe (eNB), a subframe having the lowest priority order receivedfrom the MCE is preferentially configured. When a load is generated in astate in which the base station is free from a load, or when the basestation is in a high-load state, the MBSFN subframe (eNB) may bereduced.

A specific operation example using the third modification of the firstembodiment is described with reference to FIG. 20. The same referencenumerals as those of FIG. 14, FIG. 17 and FIG. 18 denote thecorresponding portions, which are not described.

In this operation example, a priority order of a subframe set as theMBSFN subframe (MCE) is semi-statically determined, and a case where theMCE performs notification to the base station being served thereby byusing the M2 interface is disclosed below.

In Step ST2001, the MCE notifies a base station (eNB1) being servedthereby of a priority order of a subframe set as the MBSFN subframe(MCE). In this operation example, it is assumed that notification of apriority order shown in FIG. 19 is performed.

In Step ST2002, the MCE notifies a base station (eNB2) being servedthereby of a priority order of a subframe set as the MBSFN subframe(MCE). The MCE may notify all the base stations that perform the sameMBMS transmission and are served thereby of the priority order of thesubframes set as the same MBSFN subframe (MCE).

In this operation example, the MBSFN subframe (MCE) notified in StepST1401 and Step ST1402 are defined as #1 and #2. By the base station(eNB1), it is assumed that #1 and #2 have been already selected as theMBSFN subframes (eNB). More specifically, the MBSFN subframes (UE) givenfrom the base station (eNB1) to the user equipment being served therebyare #1 and #2.

In Step ST2003, the base station (eNB1) judges whether or not the MBSFNsubframe (eNB) must be added. When the addition is required, the flowshifts to Step ST2004. When the addition is not required, the flowshifts to Step ST2005.

Subsequently, a case where the base station (eNB1) increases the MBSFNsubframe (eNB) is described first. More specifically, in Step ST2003,since the base station (eNB1) judges that the MBSFN subframe (eNB) mustbe added, the flow shifts to Step ST2004.

In Step ST2004, the base station (eNB1) selects, from subframes exceptfor the subframe currently used as the MBSFN subframe (eNB), a subframethat is configured as the MBSFN subframe (MCE) received in Step ST2002and has the highest priority order of the subframes as the MBSFNsubframe (eNB). In this operation example, the MBSFN subframes currentlyused as the MBSFN subframes (eNB) are #1 and #2. Thus, of subframesexcept for the subframe currently used as the MBSFN subframe (eNB), asubframe that is configured as the MBSFN subframe (MCE) and has thehighest priority order of the subframes is “#6” (see FIG. 19).

In this manner, the MBSFN subframes (UE) “#1 and #2” are updated to “#1,#2 and #6”. Thus, in Step ST1707, the base station (eNB1) judges thatthe MBSFN subframe (UE) must be updated, and processes subsequent toStep ST1708 occur.

On the other hand, in Step ST1802, the MCE judges whether or not theMBSFN subframe (MCE) must be added. When the addition is required, theflow shifts to Step ST2006. When the addition is not required, the flowshifts to Step ST2007. In this case, it is assumed that, for example,the MCE judges that the MBSFN subframe (MCE) must be added.

In Step ST2006, the MCE selects, from subframes except for the subframecurrently used as the MBSFN subframe (MCE), a subframe that isconfigured as the MBSFN subframe (MCE) and has the highest priorityorder of the subframes as the MBSFN subframe (MCE). In this operationexample, the MBSFN subframes currently used as the MBSFN subframes (MCE)are #1 and #2. Thus, of subframes except for the subframe currently usedas the MBSFN subframe (MCE), a subframe that is configured as the MBSFNsubframe (MCE) and has the highest priority order of the subframes is“#6” (see FIG. 19).

In this manner, in Step ST1705, the MCE notifies the base station (eNB2)being served thereby of the updated MBSFN subframe (MCE) updated in StepST2006. In Step ST1706, the MCE notifies the base station (eNB1) beingserved thereby of the updated MBSFN subframe (MCE) updated in StepST2006.

In Step ST1707, the base station (eNB1) judges whether or not the MBSFNsubframe (UE) must be updated. At this time, since the MBSFN subframes(UE) have been already “#1, #2 and #6”, it is judged that the updatingneed not be performed, and a system information change does not occur.

In this manner, the MCE and the base station being served by the MCEperform adjustment depending on the same priority order to make itpossible to suppress the repetition-number of system information changeof the base station being served thereby.

Furthermore, for example, in Step ST1802, it is assumed that the MCEjudges that the MBSFN subframe (MCE) need not be added.

In Step ST2007, the MCE selects, from subframes currently used as theMBSFN subframes (MCE), a subframe that is configured as the MBSFNsubframe (MCE) and has the lowest priority order of the subframes as thesubframe that is deleted from the MBSFN subframes (MCE). In thisoperation example, the subframes currently used as the MBSFN subframes(MCE) are #1 and #2. Thus, of the subframes currently used as the MBSFNsubframes (MCE), a subframe that is configured as the MBSFN subframe(MCE) and has the lowest priority order of the subframes is “#2” (seeFIG. 19).

In this manner, in Step ST1705, the MCE notifies the base station (eNB2)being served thereby of the updated MBSFN subframe (MCE) updated in StepST2007. In Step ST1706, the MCE notifies the base station (eNB1) beingserved thereby of the updated MBSFN subframe (MCE) updated in StepST2007.

In Step ST1707, the base station (eNB1) judges whether or not the MBSFNsubframe (UE) must be updated. At this time, since the MBSFN subframes(UE) have been already “#1, #2 and #6”, it is judged that the updatingneed not be performed, and a system information change does not occur.

In this manner, the MCE and the base station being served by the MCEperform adjustment depending on the same priority order to make itpossible to suppress the repetition-number of system information changeof the base station being served thereby.

A case where the base station (eNB1) reduces the MBSFN subframe (eNB) isdescribed below. More specifically, in Step ST2003, since the basestation (eNB1) judges that the MBSFN subframe (eNB) need not be added,the flow shifts to Step ST2005.

In Step ST2005, the base station (eNB1) selects, from subframes used asthe MBSFN subframes (eNB), a subframe that is configured as the MBSFNsubframe (MCE) received in Step ST2002 and has the lowest priority orderof the subframes as the subframe deleted from the MBSFN subframes (eNB).In this operation example, the MBSFN subframes currently used as theMBSFN subframes (eNB) are #1 and #2. Thus, of the subframes currentlyused as the MBSFN subframes (eNB), a subframe that is configured as theMBSFN subframe (MCE) and has the lowest priority order of the subframesis “#2” (see FIG. 19).

The MBSFN subframes (MCE) are still “#1 and #2”. In this manner, theMBSFN subframes (UE) are “#1 and #2”, and are not updated. Thus, in StepST1707, the base station (eNB1) judges that the MBSFN subframe (UE) neednot be updated, and a system information change does not occur.

In this manner, the MCE and the base station being served by the MCEperform adjustment depending on the same priority order to make itpossible to suppress the repetition-number of system information changeof the base station being served thereby.

Note that the number of MBSFN subframes to be updated is not limited toone and may be two or more.

In the modification, an example obtained by combining the firstembodiment to the modification is mainly described. However, acombination between the first modification of the first embodiment andthe modification can be used.

The third modification of the first embodiment can achieve the effectsbelow in addition to those of the first embodiment.

When a plurality of base stations are served by the MCE, even though thenumbers of configured MBSFN subframes (eNB) of the respective basestations are different from each other, the MCE and the base stationbeing served by the MCE perform adjustment depending on the samepriority order to make it possible to minimize a change of an MBSFNsubframe configuration given from the base station to a user equipment.In this manner, a change of system information can be suppressed. Thus,reception of the system information with intermittent receptioninterruption of the user equipment can be suppressed. In this manner, anincrease in power consumption of the user equipment can be prevented.

Fourth Modification of First Embodiment

In a case where the first embodiment is used, the following problemoccurs.

Since data that must be transmitted per unit time and is related to anMBMS increases, it is discussed that the MCE changes configurations toincrease the MBSFN subframe (MCE).

By increasing MBMS data, configurations are changed to increase theMBSFN subframe (MCE) configured in the MCE. Accordingly, if any deviceis not used, the MCE may select, as an additional MBSFN subframe (MCE),the MBSFN subframe (eNB) configured by the base station being servedthereby to realize energy saving. In this case, even an MBSFN subframe(eNB) configured by the base station to realize energy saving, when thesubframe is selected as the MBSFN subframe (MCE), the base station mustperform transmission of an MCH transport channel using the MBSFN. Thus,even in the MBSFN subframe (eNB) configured to realize energy saving,transmission except for the transmission of one symbol of CRS occurs. Inthis manner, even in the MBSFN subframe (eNB) configured to realizeenergy saving, the power supply of the transmitter power amplifiercannot be turned off. A problem in which the base station cannot realizelower power consumption is posed.

A specific example that causes problems is described with reference toFIG. 21.

In Step ST1401, the MCE notifies a base station (eNB2) being servedthereby of the MBSFN subframe (MCE).

In Step ST1402, the MCE notifies a base station (eNB1) being servedthereby of the MBSFN subframe (MCE). In this specific example, it isassumed that a second subframe (#1) and a third subframe (#2) areconfigured as MBSFN subframes (MCE).

In Step ST2101, the base station (eNB1) judges whether or not an energysaving operation is executed. When it is judged that the energy savingoperation is executed, the flow shifts to Step ST1403. When it is judgedthat the energy saving operation is not executed, the judgment in StepST2101 is repeated.

In Step ST1404, the base station (eNB1) selects the MBSFN subframe(eNB). In this specific example, a subframe different from #1 and #2serving as the MBSFN subframes (MCE) is selected as the MBSFN subframe(eNB). In this operation example, for example, it is assumed that aseventh subframe (#6) and an eighth subframe (#7) are configured asMBSFN subframes (eNB).

That is, in Step ST2102, the base station (eNB1), in the subframes #1and #2, executes transmission of an MCH transport channel using theMBSFN. In Step ST2103, the base station (eNB1), in the subframes #6 and#7, executes only transmission of one symbol of CRS for lower powerconsumption and does not execute a transmitting operation in other radioresources. More specifically, the power supply of the transmitter poweramplifier or the like is turned off for except the transmission of theone symbol of CRS in the MBSFN subframe (eNB).

In Step ST1703, the MCE judges whether or not the configuration of theMBSFN subframe (MCE) must be changed. When the change is required, theflow shifts to Step ST1704. When the change is not required, thejudgment in Step ST1703 is repeated. In addition to this, it may bejudged whether or not the MBSFN subframe (MCE) must be increased. Inthis case, when the increase is required, the flow shifts to StepST1704. When the increase is not required, the judgment in Step ST1703is repeated.

In Step ST1704, the MCE updates the MBSFN subframe (MCE). In thespecific example, it is assumed that #1, #2 and #7 are selected as theMBSFN subframes (MCE). More specifically, it is assumed that #7 is addedas the MBSFN subframe (MCE).

In Step ST1705, the MCE notifies the base station (eNB2) being servedthereby of the updated MBSFN subframe (MCE) updated in Step ST1704.

In Step ST1706, the MCE notifies the base station (eNB1) being servedthereby of the updated MBSFN subframe (MCE) updated in Step ST1704.Subsequently, the eNB2 is considered to be equal to the eNB1, which isnot described.

That is, in Step ST2104, the base station (eNB1), in the subframes #1,#2 and #7, must execute transmission of an MCH transport channel usingthe MBSFN. In Step ST2105, the base station (eNB1), in the subframes #6,executes only transmission of one symbol of CRS for lower powerconsumption and does not execute a transmitting operation in other radioresources. An operation for lower power consumption is executed for onlythe subframe #6. In this manner, the base station (eNB1) is due toexecute an energy saving operation for two subframes. However, thenumber of subframes for energy saving disadvantageously reduces againstthe intension of the base station (eNB1).

As described above, if any device is not used, an effect of lower powerconsumption of the base station varies each time an amount of data ofthe MBMS varies.

A solution in the fourth modification of the first embodiment isdescribed below. Parts different from the solution of the firstembodiment are mainly described below. Undescribed parts are the same asthose in the first embodiment.

The base station notifies the MCE of an MBSFN subframe configuration ofown cell. When the MCE updates the MBSFN subframe configuration, the MCEperforms adjustment by using the information.

Notification to the MCE may be executed only when the MBSFN subframe(eNB) is configured. The notification may be performed only when asubframe different from the MBSFN subframe (MCE) is configured as theMBSFN subframe (eNB).

A specific example of the MBSFN subframe configuration of which the MCEis notified are similar to that of the second modification of the firstembodiment, which is not described.

Two specific examples of adjustment performed by the MCE are disclosedbelow. (1) When the MCE increases the MBSFN subframe (MCE), it is judgedwhether or not a subframe except for a subframe currently used as theMBSFN subframe (MCE) is present in except for the MBSFN subframe (eNB)that receives the notification from the base station. When the subframeis present, the subframe is selected as an MBSFN subframe (MCE) thatincreases the subframe. (2) When the MCE reduces the MBSFN subframe(MCE), it is judged whether or not a subframe currently used as theMBSFN subframe (MCE) is present in the MBSFN subframe (eNB) thatreceives notification from the base station. When the subframe ispresent, the subframe is selected as an MBSFN subframe (MCE) thatreduces the subframe. The adjustment may be commonly performed by aplurality of base stations being served by the MCE.

A specific example of a notification timing from the base station to theMCE is similar to that of the second modification of the firstembodiment, which is not described.

A specific example of an interface used for notification from the basestation to the MCE is similar to that of the second modification of thefirst embodiment, which is not described.

A specific operation example using the fourth modification of the firstembodiment is described with reference to FIG. 18.

In Step ST1401, the MCE notifies a base station (eNB1) being servedthereby of the MBSFN subframe (MCE).

In Step ST1402, the MCE notifies a base station (eNB2) being servedthereby of the MBSFN subframe (MCE). In this operation example, forexample, it is assumed that a second subframe (#1) and a third subframe(#2) are configured as MBSFN subframes (MCE).

In Step ST1403, the base station (eNB1) judges whether or not an energysaving operation is executed. When it is judged that the energy savingoperation is executed, the flow shifts to Step ST1404. When it is judgedthat the energy saving operation is not executed, the judgment in StepST1403 is repeated.

In Step ST1404, the base station (eNB1) selects the MBSFN subframe(eNB). In this operation example, for example, it is assumed that thethird subframe (#2), the seventh subframe (#6) and an eighth subframe(#7) are configured as MBSFN subframes (eNB).

That is, the base station (eNB1), in the subframes #1 and #2, executestransmission of an MCH transport channel using the MBSFN. In thesubframes #6 and #7, the base station executes only transmission of onesymbol of CRS and does not execute a transmitting operation in otherradio resources. More specifically, the power supply of the transmitterpower amplifier or the like is turned off for except the transmission ofthe one symbol of CRS.

In Step ST1801, the base station (eNB1) notifies the MCE of the MBSFNsubframe (eNB) as information of the MBSFN subframe configuration. Inthis operation example, the MBSFN subframes are #2, #6 and #7. Thenotification uses the M2 interface.

Subsequently, a case where the MCE increases the MBSFN subframe (MCE) isdescribed first. More specifically, in Step ST1802, since the MCE judgesthat the MBSFN subframe (MCE) must be added, the flow shifts to StepST1803.

In Step ST1803, the MCE judges whether or not a subframe except for thesubframe currently used as the MBSFN subframe (MCE) is present in exceptthe MBSFN subframe (eNB) that receives the notification from the basestation. When the subframe is present, the flow shifts to Step ST1804.When the subframe is not present, the flow shifts to Step ST1704. InStep ST1704, the MCE updates the MBSFN subframe (MCE). In this operationexample, as subframes except for the subframe currently used as theMBSFN subframe (MCE) in except the MBSFN subframe (eNB), #3 and #8 arepresent. Thus, in Step ST1803, it is judged that the subframe ispresent, and the flow shifts to Step ST1804.

In Step ST1804, the MCE selects, as a subframe added to the MBSFNsubframe (MCE), a subframe except for the subframe currently used as theMBSFN subframe (MCE) in except the MBSFN subframe (eNB). In thisoperation example, it is assumed that #8 is selected.

Even though the MBSFN subframe (MCE) is updated, by performing theprocess, the MBSFN subframe (eNB) that configured by the base station(eNB1) for energy saving is not selected as the MBSFN subframe (MCE).Thus, transmission of the MCH transport channel need not be executed inthe MBSFN subframe (eNB) configured for energy saving.

A case where the MCE reduces the MBSFN subframe (MCE) is describedbelow. More specifically, in Step ST1802, since the MCE judges that theMBSFN subframe (MCE) need not be added, the MCE shifts to Step ST1805.

In Step ST1805, the MCE judges whether or not, in the MBSFN subframe(eNB) of a base station that receives the notification from the basestation, a subframe currently used as the MBSFN subframe (MCE) ispresent. When the subframe is present, the flow shifts to Step ST1806.When the subframe is not present, the flow shifts to Step ST1704. InStep ST1704, the MCE updates the MBSFN subframe (MCE). In this operationexample, as a subframe currently used as the MBSFN subframe (MCE) in theMBSFN subframe (eNB), #2 is present. Thus, in Step ST1805, it is judgedthat the subframe is present, and the flow shifts to Step ST1806.

In Step ST1806, the MCE selects, as a subframe deleted from the MBSFNsubframe (MCE), a subframe currently used as the MBSFN subframe (MCE) inthe MBSFN subframe (eNB). In this operation example, it is assumed that#2 is selected. When the MBSFN subframe (MCE) is updated, by performingthe above process, the MBSFN subframe (eNB) configured for energy savingin the base station (eNB1) need not execute transmission of the MCHtransport channel without changing the MBSFN subframe (eNB).

Note that the number of MBSFN subframes to be updated is not limited toone and may be two or more.

In the modification, an example obtained by combining the firstembodiment to the modification is mainly described. However, acombination between the first modification of the first embodiment andthe modification can be used.

The fourth modification of the first embodiment can achieve the effectsbelow in addition to those of the first embodiment.

Even though addition of the MBSFN subframe (MCE) is required byincreasing data of the MBMS, the MCE performs adjustment to make itpossible to minimize selection of the MBSFN subframe (eNB) configured bythe base station being served by the MCE to realize energy saving as anadditional MBSFN subframe (MCE). In this manner, transmission of the MCHtransport channel can be executed in the MBSFN subframe (eNB) configuredto realize energy saving, and lower power consumption of the basestation can be achieved as an effect.

Fifth Modification of First Embodiment

In a case where the fourth modification of the first embodiment is used,a new problem occurs as follows.

A case where the MBSFN subframes (eNB) are independently configured forthe base stations being served by the MCE, respectively. In a subframeexcept for a plurality of MBSFN subframes (eNB) designated by aplurality of base stations being served by the MCE, the possibility thata subframe except for the subframe currently used as the MBSFN subframe(MCE) is not present increases. In this manner, the problem of thefourth modification of the first embodiment is posed again.

A solution in the fifth modification of the first embodiment isdescribed below. Parts different from the solution of the firstembodiment are mainly described below. Undescribed parts are the same asthose in the first embodiment.

The MCE notifies a base station being served thereby of information of apriority order of a subframe configured as the MBSFN subframe (MCE).When the base station that receives the information executes or changesa configuration of the MBSFN subframe (eNB), adjustment is performed byusing the information of the priority order. The adjustment may becommonly performed by a plurality of base stations being served by theMCE.

A specific example of information of a priority order when the fifthmodification of the first embodiment in the conventional technique isshown in FIG. 19. The description in FIG. 19 is similar to that of thethird modification of the first embodiment, which is not described.

The priority order may be statically determined or may besemi-statically determined on the network side. For example, thenotifying method to a base station being served by the MCE when thepriority order is semi-statically determined in the MCE is similar tothat of the third modification of the first embodiment, which is notdescribed.

Two specific examples of adjustment performed by the base station aredisclosed below. (1) When the base station increases the MBSFN subframe(eNB), in a subframe except for a subframe currently used in the MBSFNsubframe (eNB), a subframe having the lowest priority order receivedfrom the MCE is preferentially configured. When the base station is freefrom a load, or when the base station is in a low-loading state, theMBSFN subframe (eNB) may be increased. (2) When the base station reducesthe MBSFN subframe (eNB), in the subframe currently used as the MBSFNsubframe (eNB), a subframe having the highest priority order receivedfrom the MCE is preferentially configured. When a load is generated in astate in which the base station is free from a load, or when the basestation is in a high-load state, the MBSFN subframe (eNB) may bereduced.

A specific operation example using the fifth modification of the firstembodiment is described with reference to FIG. 20.

In this operation example, a priority order of a subframe configured asthe MBSFN subframe (MCE) is semi-statically determined, and a case wherethe MCE performs notification to the base station being served therebyby using the M2 interface is disclosed below.

In Step ST2001, the MCE notifies a base station (eNB1) being servedthereby of a priority order of a subframe configured as the MBSFNsubframe (MCE). In this operation example, it is assumed thatnotification of a priority order shown in FIG. 19 is performed.

In Step ST2002, the MCE notifies a base station (eNB2) being servedthereby of a priority order of a subframe configured as the MBSFNsubframe (MCE). The MCE may notify all the base stations that performthe same MBMS transmission and are served thereby of the priority orderof the subframes configured as the same MBSFN subframe (MCE).

In this operation example, the MBSFN subframe (MCE) notified in StepST1401 and Step ST1402 are defined as #1 and #2. By the base station(eNB1), it is assumed that #3 and #8 have been already selected as theMBSFN subframes (eNB). More specifically, the MBSFN subframes (UE)designated from the base station (eNB1) to the user equipment beingserved thereby are #1, #2, #3 and #8. That is, the base station (eNB1),in the subframes #1 and #2, executes transmission of an MCH transportchannel using the MBSFN. In order to achieve lower power consumption inthe subframes #3 and #8, only transmission of one symbol of CRS isperformed, and a transmission operation is not performed in other radioresources. More specifically, the power supply of the transmitter poweramplifier or the like is turned off for except the transmission of theone symbol of CRS.

In Step ST2003, the base station (eNB1) judges whether or not the MBSFNsubframe (eNB) must be added. When the addition is required, the flowshifts to Step ST2004. When the addition is not required, the flowshifts to Step ST2005.

Subsequently, a case wherein the base station (eNB1) increases the MBSFNsubframe (eNB) is described first. More specifically, in Step ST2003,since the base station (eNB1) judges that the MBSFN subframe (eNB) mustbe added, the flow shifts to Step ST2004.

In Step ST2004, the base station (eNB1) selects, from subframes exceptfor the subframe currently used as the MBSFN subframe (eNB), a subframethat has the lowest priority order of the subframes configured as theMBSFN subframe (MCE) received in Step ST2002 as the MBSFN subframe(eNB). In this operation example, the subframes currently used as theMBSFN subframes (eNB) are #3 and #8. Thus, of subframes except for thesubframe currently used as the MBSFN subframe (eNB), a subframe that hasthe lowest priority order of the subframes configured as the MBSFNsubframe (MCE) is “#7” (see FIG. 19). According to the process, asubframe slightly selected as the MBSFN subframe (MCE) by the MCE can bemade the MBSFN subframe (eNB) selected for energy saving. In thismanner, against the intension of the base station (eNB1), reducing thenumber of subframes for energy saving can be performed less frequently.

On the other hand, in Step ST1802, the MCE judges whether or not theMBSFN subframe (MCE) must be added. When the addition is required, theflow shifts to Step ST2006. When the addition is not required, the flowshifts to Step ST2007. In this case, it is assumed that, for example,the MCE judges that the MBSFN subframe (MCE) must be added.

In Step ST2006, the MCE selects, from subframes except for the subframecurrently used as the MBSFN subframe (MCE), a subframe that isconfigured as the MBSFN subframe (MCE) and has the highest priorityorder of the subframes as the MBSFN subframe (MCE). In this operationexample, the subframes currently used as the MBSFN subframes (MCE) are#1 and #2. Thus, of subframes except for the subframe currently used asthe MBSFN subframe (MCE), a subframe that is configured as the MBSFNsubframe (MCE) and has the highest priority order of the subframes is“#6” (see FIG. 19).

In this manner, in Step ST1705, the MCE notifies the base station (eNB2)being served thereby of the updated MBSFN subframe (MCE) updated in StepST2006. In Step ST1706, the MCE notifies the base station (eNB1) beingserved thereby of the updated MBSFN subframe (MCE) updated in StepST2006.

The base station (eNB1) executes transmission of an MCH transportchannel about not only #1 and #2 but also #6. However, thus, thesubframes do not overlap #7, #3 and #8 that are the MBSFN subframes(eNB) configured to realize energy saving.

In this manner, the MCE and the base station being served by the MCEperform adjustment depending on the same priority order to make itpossible to realize designed lower power consumption of the base stationbeing served thereby.

Furthermore, for example, in Step ST1802, it is assumed that the MCEjudges that the MBSFN subframe (MCE) need not be added.

In Step ST2007, the MCE selects, from subframes currently used as theMBSFN subframes (MCE), a subframe that is configured as the MBSFNsubframe (MCE) and has the lowest priority order of the subframes as thesubframe that is deleted from the MBSFN subframes (MCE). In thisoperation example, the subframes currently used as the MBSFN subframes(MCE) are #1 and #2. Thus, of the subframes currently used as the MBSFNsubframes (MCE), a subframe that is configured as the MBSFN subframe(MCE) and has the lowest priority order of the subframes is “#2” (seeFIG. 19).

In this manner, in Step ST1705, the MCE notifies the base station (eNB2)being served thereby of the updated MBSFN subframe (MCE) updated in StepST2007. In Step ST1706, the MCE notifies the base station (eNB1) beingserved thereby of the updated MBSFN subframe (MCE) updated in StepST2007.

The base station (eNB1) executes transmission of an MCH transportchannel in #1. However, thus, #7, #3 and #8 that are the MBSFN subframes(eNB) configured to realize energy saving are not influenced.

In this manner, the MCE and the base station being served by the MCEperform adjustment depending on the same priority order to make itpossible to realize designed lower power consumption of the base stationbeing served thereby.

A case where the base station (eNB1) reduces the MBSFN subframe (eNB) isdescribed below. More specifically, in Step ST2003, since the basestation (eNB1) judges that the MBSFN subframe (eNB) need not be added,the flow shifts to Step ST2005.

In Step ST2005, the base station (eNB1) selects, from subframescurrently used as the MBSFN subframes (eNB), a subframe that isconfigured as the MBSFN subframe (MCE) received in Step ST2002 and hasthe highest priority order of the subframes as the subframe deleted fromthe MBSFN subframes (eNB). In this operation example, the subframescurrently used as the MBSFN subframes (eNB) are #3 and #8. Thus, of thesubframes currently used as the MBSFN subframes (eNB), a subframe thatis configured as the MBSFN subframe (MCE) and has the highest priorityorder of the subframes is “#3” (see FIG. 19).

Subframes that are configured as the MBSFN subframes (MCE) and havehigher priority orders are deleted from the MBSFN subframes for energysaving, more stable lower power consumption of a base station that isnot easily influenced by the addition of the MBSFN subframe (MCE) by anincrease of MBMS data can be realized.

In this manner, the MCE and the base station being served by the MCEperform adjustment depending on the same priority order to make itpossible to realize designed lower power consumption of the base stationbeing served thereby.

Note that the number of MBSFN subframes to be updated is not limited toone and may be two or more.

In the modification, an example obtained by combining the firstembodiment to the modification is mainly described. However, acombination between the first modification of the first embodiment andthe modification can be used.

The fifth modification of the first embodiment can achieve the effectsbelow in addition to those of the first embodiment.

When a plurality of base stations are served by the MCE, even though thenumbers of configured MBSFN subframes (eNB) of the respective basestations are different from each other, the MCE and the base stationbeing served by the MCE perform adjustment depending on the samepriority order to make it possible to minimize selection of the MBSFNsubframe (eNB) configured to realize energy saving by the base stationas the added MBSFN subframe (MCE). In this manner, transmission of theMCH transport channel can be executed in the MBSFN subframe (eNB)configured to realize energy saving, and lower power consumption of thebase station can be achieved as an effect.

It may be statically or semi-statically determined as a mobilecommunication system whether adjustment (the second modification of thefirst embodiment and the third modification of the first embodiment)that reduces the change of the system information or adjustment (thefourth modification of the first embodiment and the fifth modificationof the first embodiment) that can easily obtain the effect of energysaving should be performed.

When the determination is semi-statically made, two specific examples ofa main body that determines whether or not one of the adjusting methodsshould be selected are disclosed below. (1) The MCE makes adetermination. (2) The MME makes a determination.

A base station being served by the MCE is notified of the adjustingmethod used when the MCE makes a determination by using the M2interface. Alternatively, the MME is notified of the adjusting method byusing the M3 interface, and the base station being served thereby isnotified of the adjusting method by using the S1 interface.

A base station being served by the MCE is notified of the adjustingmethod used when the MME makes a determination by using the S1interface.

Second Embodiment

A problem to be solved by a second embodiment is described below.

Non-Patent Document 11 discloses that CRS transmission is made lessfrequent to save a network power to make it possible to configure alarger number of MBSFN subframes. However, a concrete main subject ofthe configuration, whether or not a larger number of MBSFN subframes canbe configured, and a concrete method of increasing the number of MBSFNsubframes are not disclosed.

In the embodiment, a concrete method that can configure a larger numberof MBSFN subframes is disclosed below.

A solution in the second embodiment is described below.

In the conventional technique, as the MBSFN subframes, a maximum of sixsubframes can be configured in one radio frame (Non-Patent Document 2).

In the second embodiment, MBSFN subframes the number of which is largerthan that in the conventional technique can be configured in one radioframe. More specifically, subframes the number of which is larger than 6can be configured in one radio frame as MBSFN subframes. A subframeexcept for a subframe that can transmits the P-SS, the S-SS and the BCHcan be configured as an MBSFN subframe. In this manner, lower powerconsumption can be enhanced while maintaining transmission of the P-SS,the S-SS and the BCH serving as signals used in cell-search. A subframeexcept for the first subframe (#0) and the sixth subframe (#5) can beconfigured as the MBSFN subframe. In the conventional technique, #0 and#5 are radio resources to which the P-SS, the S-SS and the BCH aremapped. Thus, in this manner, lower power consumption can be enhancedwhile maintaining transmission of the P-SS, the S-SS and the BCH servingas signals used in cell-search.

As the MBSFN subframes, a maximum of eight subframes can be configuredin one radio frame. A maximum of eight subframes except for the firstsubframe (#0) and the sixth subframe (#5) can be configured as the MBSFNsubframes.

The second embodiment can be used in combination with the firstembodiment, the first modification of the first embodiment, the secondmodification of the first embodiment, the third modification of thefirst embodiment, the fourth modification of the first embodiment andthe fifth modification of the first embodiment.

The second embodiment can achieve effects below.

Effective lower power consumption achieved by a base station can berealized while maintaining transmission of the CRS, the P-SS/S-SS andthe BCH serving as necessary signals in a downlink for an inactive userequipment (no-active UE).

First Modification of Second Embodiment

In a case where the second embodiment is used, a new problem occurs asfollows.

In a PDCCH that schedules a paging message, a subframe in which a P-RNTI(Paging Radio Network Temporary Identifier) may be present is referredto as paging occasion (PO) (Non-Patent Document 3). An occurrencepattern of paging occasion is as shown in FIG. 22 (Non-Patent Document3). Parameters in FIG. 22 are described below with reference toEquations (1), (2) and (3).Ns=max(1,nB/T)  Equation (1)UE_ID=IMSI mod 1024  Equation (2)N=min(T,nB)  Equation (3)i_s=floor(UE_ID/N)mod Ns  Equation (4)The “T” included in Equation (1) is DRX (Discontinuous Reception) cycleof a user equipment. The “T” is determined by a DRX value unique to theshortest user equipment if allocation is performed by a higher layer,and an initial DRX value is broadcasted in the system information. Ifthe DRX unique to the user equipment is set by the higher-level layer,the initial value is applied. The “nB” included in Equation (1) isbroadcasted in the system information. As the “nB”, 4T, 2T, T, T/2, T/4,T/8, T/16 and T/32 are given. The “Ns” is given as the large one of 1and nB/T according to Equation (1).

The “IMSI” included in Equation (2) is an international mobilesubscriber identity. The “UE-ID” is given as a remainder obtained whenthe IMSI is divided by “1024” according to Equation (2).

The “N” is given as the small one of T and nB according to Equation (3).

The “i_s” is given as a remainder obtained when a value obtained bydividing UE-ID by N (rounded value) is divided by Ns according toEquation (4).

More specifically, when the second embodiment is executed without anydevice, for example, when a paging occasion is a subframe number #9 or#4, the base station cannot notify the user equipment of paging becausethe base station is in a lower power consumption state.

A solution in the first modification of the second embodiment isdescribed below.

When the base station receives a paging message from the MME, the basestation releases the energy saving operation. Alternatively, when thebase station receives the paging message from the MME, the base stationmay set the number of subframes that can be set in one radio frame to anumber of the conventional technique. Alternatively, when the basestation receives the paging message from the MME, the base station mayset the number of subframes that can be set in one radio frame to six asin the conventional technique.

In the first modification of the second embodiment, a combination to thesecond embodiment is mainly described. However, combinations to thefirst embodiment, the first modification of the first embodiment, thesecond modification of the first embodiment, the third modification ofthe first embodiment, the fourth modification of the first embodimentand the fifth modification of the first embodiment can be used.

The first modification of the second embodiment can achieve the effectsbelow in addition to those of the second embodiment. Effective lowerpower consumption achieved by the base station can be realized whilesolving a problem in which notification of the paging to the userequipment cannot be performed.

Second Modification of Second Embodiment

In the second modification of the second embodiment, the same problem asthat in the first modification of the second embodiment is solved by amethod different from that in the first modification of the secondembodiment.

A solution in the second modification of the second embodiment isdescribed below.

The base station can use a subframe except for the paging occasion asthe MBSFN subframe. A subframe except for the subframes corresponding tothe P-SS, the S-SS, and the paging occasion can also be used as theMBSFN subframe.

A specific example of a method of selecting a subframe except for thepaging occasion is described below. It is assumed that the techniquedisclosed in the second modification of the second embodiment is appliedto the conventional technique. As described in the first modification ofthe second embodiment, “Ns” is determined by the parameters “T” and“nB”. The base station broadcasts the parameters “T” and “nB” to theuser equipment being served thereby using the system information. Thus,the base station can know the values of “T” and “nB”. From the values,the base station can also know the value of “Ns”. By the value of Ns, anoccurrence pattern of the paging occasion in FIG. 22 is confirmed. Forexample, when “Ns” is “1”, the paging occasion is only the subframenumber #9. When “Ns” is “2”, the paging occasions are the subframenumbers #4 and #9. When “Ns” is “4”, the paging occasions are subframenumbers #0 and #4, #5 and #9. As described above, the base stationconfirms the parameters “T” and “nB” of own cell to calculate “Ns”,confirms the subframe number of the paging occasion, and selects asubframe except for the paging occasion.

As the MBSFN subframes, a maximum of seven subframes can be configuredin one radio frame. A maximum of seven subframes except for the firstsubframe (#0), the sixth subframe (#5) and the tenth subframe (#9) canbe configured as the MBSFN subframes. This is because, even though “Ns”has any value, the subframe number #9 corresponds to the paging occasion(see FIG. 22). The base station can use a subframe except for the pagingoccasion as the MBSFN subframe.

In the second modification of the second embodiment, a combination tothe second embodiment is mainly described. However, combinations to thefirst embodiment, the first modification of the first embodiment, thesecond modification of the first embodiment, the third modification ofthe first embodiment, the fourth modification of the first embodimentand the fifth modification of the first embodiment can be used.

The second modification of the second embodiment can achieve the effectsbelow in addition to those of the second embodiment. Effective lowerpower consumption in which an energy saving operation is not executeduselessly can be realized while solving a problem in which notificationof the paging to the user equipment cannot be performed.

Third Embodiment

A problem to be solved by a third embodiment is described below.

In the conventional technique, an MBSFN (Multimedia Broadcast multicastservice Single Frequency Network) is supported for the MCH transportchannel (Non-Patent Document 1). In an MBSFN synchronization area, allbase station belonging to the area are synchronized with each other, andMBSFN transmission can be executed (Non-Patent Document 1). Transmissionusing the MBSFN is transmitted in the MBSFN subframe. The MBSFNsynchronization area is semi-statically configured by, for example, anoperator (Non-Patent Document 1).

More specifically, in the conventional technique, in order to cause thebase station to configure the MBSFN subframe, the base station mustbelong to the MBSFN synchronization area. A problem in which a basestation that does not belong to the MBSFN synchronization area cannotexecute an energy saving operation using the MBSFN subframe is posed.

A solution in the third embodiment is described below.

Even the base station that does not belong to the MBSFN synchronizationarea can configure the MBSFN subframe to a user equipment being servedthereby. Alternatively, even the base station that is not connected tothe MCE can configure the MBSFN subframe to a user equipment beingserved thereby. Alternatively, even the base station that does notreceive a configuration related to the MBSFN subframe from the MCE canconfigure the MBSFN subframe to a user equipment being served thereby.

The third embodiment can be used in combination with the firstembodiment, the first modification of the first embodiment, the secondmodification of the first embodiment, the third modification of thefirst embodiment, the fourth modification of the first embodiment, thefifth modification of the first embodiment, the second embodiment, thefirst modification of the second embodiment and the second modificationof the second embodiment.

Cases where the third embodiment is combined to the second modificationof the first embodiment and the fourth modification of the firstembodiment are described below. In the second modification of the firstembodiment and the fourth modification of the first embodiment, the basestation notifies the MCE of the MBSFN subframe configuration of own cellby using the M2 interface. In the combination with the third embodiment,the M2 interface is not present. Thus, the base station notifies the MMEof the MBSFN subframe configuration of own cell by using the S1interface. The MME notifies the MCE of the MBSFN subframe configurationof the cell by using an M3 interface.

A specific operation example using a combination between the thirdembodiment and the first modification of the first embodiment isdescribed with reference to FIG. 23. The same reference numerals asthose of FIG. 14 and FIG. 16 denote the corresponding portions, whichare not described. Location is the same as the location described withreference to FIG. 15, which are not described. A neighbor cell isnotified of the MBSFN subframe configuration of own cell. In thisoperation example, a case where information representing whether or nota subframe different from a subframe indicated by the MCE of thespecific example (4) is configured as an MBSFN subframe configuration isused in the MBSFN subframe configuration of which the neighbor cell isnotified is disclosed. A case where, in an interface used fornotification to the neighbor cells, the base station of the specificexample (2) uses the S1 interface to the MME, and the MME uses the S1interface to the neighbor cells of the base station is disclosed. A casewhere a base station including the base station of the specific example(5) as a neighbor cell is selected by a method of selecting a neighborcell is disclosed. A case where the MME of the specific example (2) isused as a main subject that updates neighbor cell information isdisclosed.

In Step ST2301, the base station (eNB1) selects the MBSFN subframe(eNB). In this operation example, for example, it is assumed that theseventh subframe (#6) and the eighth subframe (#7) are configured asMBSFN subframes (eNB).

In Step ST2302, the user equipment operates using the MBSFN subframe(eNB) received in Step ST1406 as a subframe reserved for the MBSFN in adownlink. In this operation example, the user equipment operates using#6 and #7 as subframes reserved for the MBSFN in a downlink.

In the Step ST2303, the base station (eNB1) notifies the MME ofinformation representing whether or not a subframe different from asubframe indicated by the MCE is configured as an MBSFN subframeconfiguration as information of the MBSFN subframe configuration. Inthis operation example, a subframe different from a subframe indicatedby the MCE is configured as the MBSFN subframe configuration isnotified. The S1 interface is used for the notification.

In Step ST2304, the MME updates the neighbor cell information of thebase station selected in Step ST1602. Information representing whetheror not the MBSFN serving as the neighbor cell information is supportedis updated. The MME may perform determination of the update based on theinformation received in Step ST2303. In Step ST2303, the MME can judgethat the eNB1 has configured a subframe different from a subframeindicated by the MCE as an MBSFN subframe configuration. Thus, the MMEchanges (updates) the information representing whether or not the MBSFNserving as the neighbor cell information of the eNB2 is supported intoinformation representing that the same MBSFN subframe configuration asthat of the serving cell (eNB2) is not included in all the neighborcells. If a conventional technique is used as the neighbor cellinformation, the information is changed (updated) into “00”.

In Step ST1604, the MME notifies the base station selected in StepST1602 of the neighbor cell information updated in Step ST2304. The S1interface may be used for the notification.

In Step ST1605, the eNB2 (103-2) that receives the updated neighbor cellinformation notifies the user equipment 2 being served thereby of theupdated neighbor cell information.

In Step ST1607, the user equipment 2 that receives the updated neighborcell information performs neighbor cell measurement by using the updatedneighbor cell information. As a specific example, the user equipment 2performs the neighbor cell measurement on the assumption that a basestation that performs an MBSFN subframe configuration different fromthat of the serving cell (eNB2) is included in the neighbor cells.

The third embodiment can achieve the effects below.

Even a base station that does not belong to the MBSFN synchronizationarea can execute an energy saving operation using the MBSFN subframe.

In addition, in discussion of a current 3GPP, it is determined that theHeNB does not support the MBMS (Non-Patent Document 1). Thus, in themobile communication system, the HeNB does not belong to the MBSFNsynchronization area and the HeNB is not connected to the MCE. Even inthe system, according to the third embodiment, the HeNB can alsoconfigure the MBSFN subframe. Thus, the HeNB can also realize energysaving using the MBSFN subframe.

In this manner, an effect that an energy saving operation performed by abase station like the HeNB that does not belong to the MBSFNsynchronization area can be realized while obtaining an effect ofmaintaining downward compatibility using the MBSFN subframe can beobtained. It is assumed that the HeNBs the number of which is largerthan the number of macro cells are installed. The feasibility of theenergy saving operation of the HeNB considerably contributes to lowerpower consumption on the network side.

First Modification of Third Embodiment

A problem to be solved by a first modification of the third embodimentis described below.

In a case where the third embodiment is executed, a problem occurs asfollows.

In particular, when the third embodiment is used in combination with thefirst modification of the first embodiment, even though informationrepresenting whether or not the MBSFN is supported as the neighbor cellinformation is “00”, a case where the neighbor cell belongs to the MBSFNsynchronization area or a case where the neighbor cell does not belongto the MBSFN synchronization area is conceivable.

When all cells included in the neighbor cell information belong to thesame MBSFN synchronization area as that of own cell, a user equipmentthat receives the neighbor cell information can omit a synchronizationprocedure with the neighbor cells. For example, a description isperformed by using a flow chart showing an outline from cell search toan idle state operation performed by a user equipment (UE) in the LTEcommunication system shown in FIG. 12. If all the cells included in theneighbor cell information belong to the same MBSFN synchronization areaas that of own cell, all the cells included in the neighbor cellinformation may be synchronized with own cell. That is, the Step ST1201in which a slot timing and a frame timing are synchronized respectivelycan be omitted.

When all cells included in the neighbor cell information belong to thesame MBSFN synchronization area as that of own cell, a user equipmentthat receives the neighbor cell information can not omit asynchronization procedure with the neighbor cells in neighbor cellmeasurement.

However, when notification of the information “00” representing whetheror not the MBSFN is supported as neighbor cell information is performed,a user equipment being served by the cell cannot have the way of knowingwhether or not a cell that does not belong to the MBSFN synchronizationarea is included in the cells included in the neighbor cell information.

Thus, when the information “00” representing whether or not the MBSFN issupported as neighbor cell information is received, the user equipmentcannot omit the synchronization procedure with a neighbor cell. In thismanner, even in a state in which the synchronization procedure can beoriginally omitted, more specifically, even though all the cellsincluded in the neighbor cell information belong to the same MBSFNsynchronization area as that of own cell, the user equipment mustperform the synchronization procedure with the neighbor cell.

As described above, an useless operation occurs in cell search of a userequipment or neighbor cell measurement.

A solution in the first modification of the third embodiment isdescribed below.

Information of an MBSFN synchronization area of a neighbor cell is newlyset. The base station notifies neighbor cells of information of an MBSFNsynchronization area of own cell. Notification to the neighbor cells maybe executed only when the MBSFN subframe (eNB) is configured. On thebasis of the information, the information of the MBSFN synchronizationarea of the neighbor cell is updated, and the updated information isnotified to the user equipment being served by the base station theconfiguration notified. The user equipment that receives the broadcastinformation judges whether or not a synchronization procedure with theneighbor cell is executed on the basis of the broadcast information.

Three specific examples of information of an MBSFN synchronization areaof the neighbor cell are disclosed below. (1) Information representingwhether or not the neighbor cell includes a cell that does not belong tothe MBSFN synchronization area. (2) Information representing that theneighbor cell includes a cell that does not belong to the MBSFNsynchronization area. (3) Information representing that the neighborcell does not include a cell that does not belong to the MBSFNsynchronization area.

The user equipment may be notified of information of the MBSFNsynchronization area of the neighbor cell by using the broadcastinformation. The information may be newly set in SIB3 in the broadcastinformation, SIB5 in the broadcast information or a measurement object.The user equipment may be notified of the information. The informationmay be newly set in a neighbor cell configuration (NeighCellConfig). Theuser equipment can receive parameters used in the neighbor cellmeasurement or the like at once, and effects such as a reduction inprocessing load or prevention of control delay of the user equipment canbe obtained.

Three specific examples of information of an MBSFN synchronization areaof own cell are disclosed below. (1) Information representing whether ornot own cell belongs to the MBSFN synchronization area. (2) Informationrepresenting that own cell does not belong to the MBSFN synchronizationarea. (3) Information representing that own cell belongs to the MBSFNsynchronization area.

A specific example of judgment based on the information of the MBSFNsynchronization area of a neighbor cell of a user equipment is disclosedbelow. When the neighbor cell includes a cell that does not belong tothe MBSFN synchronization area, a synchronization procedure with theneighbor cell is performed. When the neighbor cell does not include acell that does not belong to the MBSFN synchronization area, asynchronization procedure with the neighbor cell is omitted.

A specific example of an interface used for notification to a neighborcell is the same as that in the first modification of the firstembodiment, which is not described.

A specific example of a method of selecting a neighbor cell is the sameas that in the first modification of the first embodiment, which is notdescribed.

A specific example of a main subject that updates neighbor cellinformation is the same as that in the first modification of the firstembodiment, which is not described.

A specific operation example using the first modification of the thirdembodiment is described with reference to FIG. 24.

The same reference numerals as those of FIG. 14, FIG. 16 and FIG. 23denote the corresponding portions, which are not described. Location isthe same as the location described with reference to FIG. 15, which arenot described. In this operation example, a case where, in an interfaceused for notification to the neighbor cells, the base station of thespecific example (2) uses the S1 interface to the MME, and the MME usesthe S1 interface to the neighbor cells of the base station is disclosed.A case where a base station including the base station of the specificexample (5) as the neighbor cell is selected by a method of selecting aneighbor cell is disclosed.

In Step ST2401, the base station (eNB1) notifies the MME of theinformation of the MBSFN synchronization area. In this operationexample, it is assumed that the base station (eNB1) does not belong tothe MBSFN synchronization area. In Step ST2401, the base station (eNB1)notifies the MME of the information representing that the base stationdoes not belong to the MBSFN synchronization area. The S1 interface isused for the notification.

In Step ST2304, the MME updates the neighbor cell information of thebase station selected in Step ST1602. Furthermore, the information ofthe MBSFN synchronization area of a neighbor cell of the base stationselected in Step ST1602 is updated. For example, the neighbor cellconfiguration (NeighCellConfig) is updated. The MME may performdetermination of the update based on the information received in StepST2401. In Step ST2401, the MME receives the information representingthat the base station does not belong to the MBSFN synchronization areafrom the eNB1. Thus, the MME changes (updates) the information of theMBSFN synchronization area of the neighbor cells of the eNB2 intoinformation representing that the neighbor cells include a cell thatdoes not belong to the MBSFN synchronization area.

In Step ST2402, the user equipment 2 that receives the updated neighborcell information judges whether or not the neighbor cells include a cellthat does not belong to the MBSFN synchronization area by using theupdated neighbor cell information. When it is judged that the neighborcells include a cell that does not belong to the MBSFN synchronizationarea, the flow shifts to Step ST2403. When it is judged that theneighbor cells do not include a cell that does not belong to the MBSFNsynchronization area, the flow shifts to Step ST2404.

In Step ST2403, the user equipment 2 executes a synchronizationprocedure with a neighbor cell in neighbor cell measurement.

In Step ST2404, the user equipment 2 omits the synchronization procedurein neighbor cell measurement.

In the first modification of the third embodiment, a combination to thethird embodiment is mainly described. However, combinations to the firstembodiment, the first modification of the first embodiment, the secondmodification of the first embodiment, the third modification of thefirst embodiment, the fourth modification of the first embodiment, thefifth modification of the first embodiment, the second embodiment, thefirst modification of the second embodiment and the second modificationof the second embodiment can be used.

The first modification of the third embodiment can achieve the effectsbelow in addition to those of the third embodiment.

Information of the MBSFN synchronization area of the neighbor cell isnewly set to make it possible to cause the user equipment to recognizethe information of the MBSFN synchronization area of the neighbor cell.In this manner, on the basis of the information of the MBSFNsynchronization area of the neighbor cell, the user equipment can judgewhether or not the synchronization procedure with the neighbor cell isexecuted in neighbor cell measurement or the like. An useless operationcan be omitted in cell search or neighbor cell measurement of the userequipment. Effects such as lower power consumption of a user equipmentand a reduction in control delay can be obtained.

Second Modification of Third Embodiment

A problem to be solved by a second modification of the third embodimentis described below.

In a case where the first modification of the third embodiment isexecuted, a problem occurs as follows.

When own cell does not belong to the MBSFN synchronization area, eventhough a user equipment being served thereby receives the information ofthe MBSFN synchronization area of the neighbor cell as broadcastinformation, a problem occurs as follows.

A case where, when the information of the MBSFN synchronization area ofthe neighbor cell represents that the neighbor cells do not include acell that does not belong to the MBSFN synchronization area, by usingthe first modification of the third embodiment, a user equipment beingserved by own cell omits a synchronization procedure with the neighborcell is considered. In this case, since own cell does not belong to theMBSFN synchronization area, own cell is not synchronized with theneighbor cell. Thus, on the assumption that synchronization is executed,the user equipment fails in search for a neighbor cell in neighbor cellmeasurement of the user equipment that omits the synchronizationprocess. In this manner, a power consumption of the user equipmentincreases, and a problem of an increase in control delay occurs.

A solution in the second modification of the third embodiment isdescribed below.

Information of the MBSFN synchronization area of own cell is newly set.

A user equipment that receives the information of the MBSFNsynchronization area of own cell and the information of the MBSFNsynchronization area of the neighbor cell disclosed in the firstmodification of the third embodiment judges whether or not asynchronization procedure with the neighbor cell is performed on thebasis of the two pieces of information. Alternatively, the userequipment that receives the information of the MBSFN synchronizationarea of own cell may judge whether or not the synchronization procedurewith the neighbor cell on the basis of the information.

Three specific examples of the information of the MBSFN synchronizationarea of own cell are disclosed below. (1) Information representingwhether or not own cell belongs to the MBSFN synchronization area. (2)Information representing that own cell does not belong to the MBSFNsynchronization area. (3) Information representing that own cell belongsto the MBSFN synchronization area.

The base station may notify information of the MBSFN synchronizationarea of own cell of the user equipment being served thereby by using thebroadcast information.

The information may be newly set in the SIB2 in the broadcastinformation. In the conventional technique, an MBSFN subframeconfiguration is mapped to the SIB2 (Non-Patent Document 2). Thus, theuser equipment can acquire information related to the MBSFN subframe byperforming a receiving process once, and an effect of preventing controldelay of the user equipment can be obtained.

The information may be newly set in the SIB3, the SIB4 or the SIB5 inthe broadcast information. In the conventional technique, informationrelated to cell reselect is mapped to the SIB3, the SIB4 and the SIB5(Non-Patent Document 2). The information of the MBSFN synchronizationarea of own cell in the second modification of the third embodiment isused when it is judged whether or not the synchronization procedure withthe neighbor cell is performed in the user equipment. More specifically,the information of the MBSFN synchronization area of own cell may alsobe information related to measurement of a neighbor cell in a userequipment. Thus, the user equipment can acquire information related tothe measurement of the neighbor cell by performing a receiving processonce, and an effect of preventing control delay of the user equipmentcan be obtained.

Alternatively, another piece of information may mean “information of anMBSFN area of own cell” without newly setting the information of theMBSFN area of own cell. In this manner, new information need not beadded, and a mobile communication system having excellent downwardcompatibility can be structured. Effective utilization of a radioresource can be advantageously obtained.

Two specific examples of the other piece of information are disclosedbelow. (1) In the conventional technique, information required toacquire MBMS control information is mapped to SIB13 (Non-Patent Document2). In the conventional technique, in order to cause the base station toconfigure the MBSFN subframe, the base station must belong to the MBSFNsynchronization area. Thus, when the SIB13 is broadcasted, it is assumedthat the base station represents that the base station “belongs to theMBSFN synchronization area”. On the other hand, when the SIB13 is notbroadcasted, it is assumed that the base station represents that thebase station “does not belong to the MBSFN synchronization area”. (2) Inthe conventional technique, the name of HeNB is mapped to SIB9(Non-Patent Document 2). It is determined that the HeNB does not supportthe MBMS (Non-Patent Document 1). Thus, the HeNB does not have theconfiguration of the mobile communication system belonging to the MBSFNsynchronization area. Thus, when the SIB9 is broadcasted, it is assumedthat the base station represents that the base station “does not belongto the MBSFN synchronization area”.

A specific operation example using the second modification of the thirdembodiment is described with reference to FIG. 25.

The same reference numerals as those of FIG. 14, FIG. 16, FIG. 23 andFIG. 24 denote the corresponding portions, which are not described.Location is the same as the location described with reference to FIG.15, which are not described. In this operation example, a case where, inan interface used for notification to the neighbor cells, the basestation of the specific example (2) uses the S1 interface to the MME,and the MME uses the S1 interface to the neighbor cells of the basestation is disclosed. A case where a base station including the basestation of the specific example (5) as a neighbor cell is selected by amethod of selecting a neighbor cell is disclosed.

In Step ST2501, the base station (eNB2) judges whether or not own cellbelongs to the MBSFN synchronization area.

In Step ST2502, the eNB2 (103-2) notifies the user equipment 2 beingserved thereby of the information of the MBSFN synchronization area ofown cell judged in Step ST2501.

In Step ST2503, the user equipment 2 that receives information of anMBSFN synchronization area of a serving cell in Step ST2502 judgeswhether or not the serving cell belongs to the MBSFN synchronizationarea by using the information. When it is judged that the serving cellbelongs to the MBSFN synchronization area, the flow shifts to StepST2402. When it is judged that the serving cell does not belong to theMBSFN synchronization area, the flow shifts to Step ST2404. The judgmentin Step ST2402 may be omitted.

In the second modification of the third embodiment, a combination to thethird embodiment and the first modification of the third embodiment ismainly described. However, combinations to the first embodiment, thefirst modification of the first embodiment, the second modification ofthe first embodiment, the third modification of the first embodiment,the fourth modification of the first embodiment, the fifth modificationof the first embodiment, the second embodiment, the first modificationof the second embodiment and the second modification of the secondembodiment can be used.

The second modification of the third embodiment can achieve the effectsbelow in addition to those of the third embodiment.

Information of the MBSFN synchronization area of own cell is newly setto make it possible to cause the user equipment to recognize theinformation of the MBSFN synchronization area of the serving cell. Inthis manner, on the basis of the information of the MBSFNsynchronization area of own cell, the user equipment can judge whetheror not the synchronization procedure with the neighbor cell is executedin neighbor cell measurement or the like. An useless operation can beomitted in cell search or neighbor cell measurement of the userequipment. Effects such as lower power consumption of a user equipmentand a reduction in control delay can be obtained.

One or more MBSFN resources can be used for one or more purposes. As aspecific example of a purpose using the MBSFN resource, an MBMS orpositioning is known (Non-Patent Document 1).

For example, it is discussed that the MBSFN resource is used for abackhaul link which is set between a donor cell and a relay node. Evenin a case where the MBSFN subframe is used as the backhaul link, thefirst embodiment to the third embodiment including modifications can beapplied. The number of relay nodes being served by a donor cell and thenumber of user equipments being served by a relay node vary. That is, aradio resource required for the backhaul link may change depending ondonor cells. By using the present invention, the radio resource requiredfor the backhaul link can be set by the donor cells, respectively.

Fourth Embodiment

Up to the second modification of the third embodiment, the case usingthe MBSFN subframe for energy saving is disclosed mainly, the presentinvention can be applied to a case using the MBSFN subframe to avoiddownlink interference occurring between cells. As described above, theresource of the MBSFN subframe can be used for one or more purposes. Asa purpose except for energy saving, the MBSFN subframe may also be usedto avoid downlink interference between the cells. The present inventioncan be applied to the case.

For example, in addition to the MBSFN subframe (MBSFN subframe (MCE))configured by the MCE for multi-cell transmission disclosed in the firstembodiment, an MBSFN subframe is configured by a base station. Morespecifically, the base station has a function of configuring an MBSFNsubframe therein. The MBSFN subframe (eNB) configured by the basestation is used to avoid downlink interference between the cells. Asanother example, even a base station that is disclosed in the thirdembodiment and does not have a configuration related to the MBSFNsubframe from the MCE for multi-cell transmission configures an MBSFNsubframe. More specifically, the base station has a function ofconfiguring an MBSFN subframe therein. The MBSFN subframe (eNB)configured by the base station is used to avoid downlink interferencebetween the cells.

For example, in a state in which downlink interference occurs between anormal eNB (macro cell) and a low-output-power local node, e.g., a picocell, in order to avoid inter-cell downlink interference, the normal eNB(macro cell) configures an MBSFN subframe. In the macro cell, only thefirst one or two symbols in the configured MBSFN subframe are used for auni-cast, and transmission of a PMCH is not carried out in symbolsexcept for the symbols used in the uni-cast. On the other hand, as for apico cell, the MBSFN subframe configured by the normal eNB is a normalsubframe, and normal uni-cast communication is performed to a userequipment to which interference occurs as a problem. In this manner, inan MBSFN subframe that a normal base station (macro cell) hasconfigured, since PMCH transmission from the macro cell is not performedin symbols except for the symbols for uni-cast, interference to the picocell can be reduced.

Since the low-output-power local node performs uni-cast communication toa user equipment to which interference occurs as a problem in the MBSFNsubframe configured by the normal eNB (macro cell), the configuration ofthe MBSFN subframe must be recognized. As a method for the purpose, themethod to which a base station notifies a neighbor cell of an MBSFNsubframe configuration of own cell as disclosed in the present inventioncan be applied. For example, the method disclosed in the firstmodification of the first embodiment can be applied. In the firstmodification of the first embodiment, the case having neighbor cellmeasurement of a user equipment as an object is disclosed. However, tonot only the object, the present invention can also be applied to causea base station that configures an MBSFN subframe to notify a neighborbase station of the MBSFN subframe configuration in order to avoidinter-cell interference. A normal eNB (macro cell) that configures anMBSFN subframe notifies a neighbor cell of the MBSFN subframeconfiguration. A neighbor cell (low-output-power local node in theexample) that receives the notification of the MBSFN subframeconfiguration from the normal eNB (macro cell) performs scheduling theresource of the MBSFN subframe for normal uni-cast communication to auser equipment to which interference from the macro cell occurs as aproblem. In this manner, the interference from the macro cell can beavoided.

In the above description, although a pico cell is used as a cellnotified of the MBSFN subframe configuration, not only the pico cell,but also another low-power local node such as a normal base station oran HeNB may be used. Similarly, the present invention can be applied,and inter-cell downlink interference can be avoided.

As a method of selecting a neighbor base station that performsnotification of an MBSFN subframe configuration, the method disclosed inthe present invention can be applied. For example, the method in thefirst modification of the first embodiment can be applied. In additionto this, the MME may determine an MBSFN subframe and notifies a basestation that configures the MBSFN subframe of the MBSFN subframeconfiguration. The MME may receive a neighbor cell measurement resultfrom a base station (normal eNB or low-power local node) being servedthereby in advance to determine a neighbor base station which apredetermined base station should notify of the MBSFN subframeconfiguration. The base station being served by the MME may notify theMME of the neighbor cell measurement result.

For example, an HeNB is served by the MME, the HeNB performs theneighbor cell measurement and notifies the MME of the measurementresult. The neighbor cell measurement and the notification of the resultthereof by the HeNB may be performed in registration of the HeNB or maybe regularly or periodically performed.

A report of a neighbor cell measurement obtained by a user equipmentbeing served by the base station may be used without causing the basestation being served by the MME to perform neighbor cell measurement.

In this manner, when the method disclosed in the present invention isapplied when location of a cell is performed flexibly, inter-celldownlink interference can be avoided.

As a case where an MBSFN subframe is used to avoid downlink interferenceoccurring between cells, a case where the method disclosed in the firstembodiment is applied is disclosed. However, not only the firstembodiment, but also the embodiments and the modifications of thepresent invention can be applied.

In this manner, by using the method of causing a base station toconfigure an MBSFN subframe as disclosed in the present invention,inter-cell downlink interference can be avoided by using the MBSFNsubframe.

In the embodiment, as a base station that configures an MBSFN subframe,not only the eNB/NB but also another local node such as an HeNB, HNB, ora pico eNB can be applied. When any one of the local nodes is applied,the same effects obtained by applying the eNB/NB can be obtained.

Fifth Embodiment

When an MBSFN subframe is used to avoid downlink interference betweenthe cells, a base station to which interference occurs as a problem mayrequest a neighbor base station of configuration of an MBSFN subframesfor avoiding downlink interference.

The base station has received the request configures an MBSFN subframein own base station and notifies the neighbor base station of the MBSFNsubframe configuration. As the method, the method disclosed above can beapplied.

As a specific example of judgment whether or not a base station requestsa neighbor base station of configuration of an MBSFN subframe and amethod of selecting the neighbor base station, for example, the methodsdisclosed in the specific examples (1) and (2) of the method ofselecting a neighbor cell in the first modification of the firstembodiment can be applied. As another method, when a base station wantsto preferentially reserve a subframe with which the base stationperforms scheduling to a user equipment being served thereby, the basestation may judge that the base station requests a neighbor base stationof configuration of an MBSFN subframe. In this case, as the method ofselecting a neighbor base station, the methods disclosed in the specificexamples (1) to (5) of the method of selecting a neighbor cell in thefirst modification of the first embodiment can be applied.

As a specific example of an interface used to notify a neighbor basestation of an MBSFN subframe configuration request for avoiding downlinkinterference, the methods disclosed in the specific examples (1) to (3)of the interface used for notification to a neighbor cell in the firstmodification of the first embodiment can be applied. The request isincluded in a signaling message used on each interface or a signalingmessage for the request is newly set to perform notification by usingthe interfaces. In addition to the notification of the request,notification of an identifier (cell identifier) of a base stationserving as a destination of the request, a cell identifier of own cell,or a requested resource may be performed. Notification of combinationsof the identifiers and the resource may be performed. As the identifierof the base station serving as a destination or a cell identifier of owncell, a CGI, a PCI or the like may be used. As a specific example of therequested resource, the number of MBSFN subframes may be used. A basestation that receives notification of the requested resource can use thenotification as information for judgment used when the number of MBSFNsubframes is configured.

As an example, a concrete operation performed when a base station towhich interference occurs as a problem is an HeNB is shown. The HeNB,for example, by a measurement report of a user equipment being servedthereby, recognizes that reception quality from a certain base stationexceeds a predetermined threshold value. In this manner, the HeNB judgesthat the HeNB should request the base station of an MBSFN subframeconfiguration. The HeNB notifies the MME of the request message by usingthe S1 interface. When an MCE may not be connected to the HeNB becausean MBMS is not supported for the HeNB, an X2 interface is not supportedfor the HeNB. In such a case, notification to a base station can beperformed through an MME by using the S1 interface.

The HeNB may perform, in addition to the notification of the requestmessage, notification of the identifier of a base station serving as adestination. The MME that receives the request message from the HeNB andthe identifier of the base station serving as a destination canselectively notify the base station of the request message from the HeNBon the basis of the identifier of the base station. The notification ofthe message uses the S1 interface.

The base station that receives the request message from the HeNB throughthe MME configures an MBSFN subframe for avoiding inter-cell downlinkinterference. The base station that configures the MBSFN subframenotifies neighbor cells of the MBSFN subframe configuration. As a methodof selecting a neighbor base station that performs notification of theconfiguration, a method disclosed above may be used. Alternatively, theneighbor base station that is performed notification of theconfiguration may be a base station (HeNB in the example) that requestsan MBSFN subframe configuration. This is possible when notification of arequest message and a cell identifier of own base station is performed.The HeNB that receives the MBSFN subframe configuration performsscheduling a resource of the MBSFN subframe for normal uni-castcommunication to the user equipment to which interference from the basestation occurs as a problem. As the user equipment to which interferencefrom the base station occurs as a problem, a user equipment thatperforms notification of a measurement report representing thatreception quality from the base station exceeds a predeterminedthreshold value may be used. In this manner, the interference from thebase station can be avoided.

The example shows the case where the base station to which interferenceoccurs as a problem is HeNB. However, not only the HeNB, but also anormal base station or another low-power local node such as a pico cellmay be used. The present invention can be similarly applied to any oneof low-power local nodes, and inter-cell downlink interference can beavoided. A base station serving as a destination of an MBSFN subframeconfiguration request is not limited to a normal base station, and alow-power local node may be used. A base station serving as adestination of an MBSFN subframe configuration request may be a basestation having an MBSFN subframe configuration function. The basestation broadcasts information representing that whether or not own cellhas the MBSFN subframe configuration function as the system information.The base station to which an interference problem occurs may judgewhether or not the cell has the MBSFN subframe configuration function byreceiving system information of each cell in radio-wave environmentmeasurement of a neighbor cell in own base station. The judgment may beadded to the method of selecting a neighbor base station. Own basestation does not perform measurement to receive system information, anda user equipment being served thereby may receive system information ofeach cell in radio-wave environment measurement of neighbor cells toacquire information representing whether or not each of the cells hasthe MBSFN subframe configuration function. The user equipment notifies abase station by which the user equipment is served of the informationtogether with a report of measurement, and then the base station judgeswhether or not the neighbor base station has the MBSFN subframeconfiguration function. The user equipment may judge a base stationhaving the MBSFN subframe configuration function on the basis of theinformation to notify the base station of a measurement report for anMBSFN subframe configuration request that is limited to the base stationhaving the MBSFN subframe configuration function. The base station needsnot to judge whether or not the base station has the MBSFN subframeconfiguration function, and an amount of information of signaling of ameasurement report from a user equipment being served thereby or asignaling amount can be reduced.

Since the method disclosed in the embodiment is applied to make itpossible to notify a base station that causes interference of an MBSFNsubframe configuration request from a base station that is interfered,judgment of the MBSFN subframe configuration in the base station can bemore dynamically executed. Thus, inter-cell downlink interferenceavoidance using the MBSFN subframe can be more dynamically realized.

In the base station that receives a request notification of the MBSFNsubframe configuration, if an MBSFN subframe is configured in responseto the request, a radio resource allocated to a user equipment beingserved by own cell may come short. Although the radio resource allocatedto the user equipment being served by own cell come short, when theMBSFN subframe is configured, communication with the user equipmentbeing served by own cell cannot be performed to make it impossible toprovide a service. In order to solve the problem, a base station thatreceives the request notification of the MBSFN subframe configurationmay judge that the MBSFN subframe is not configured to the requestnotification of the MBSFN subframe configuration and performnotification representing that MBSFN subframe configuration is rejectedto the base station serving as a request source. In this manner,communication with the user equipment being served by own cell issecured to make it possible to provide a service.

The shortage of the radio resource may not be the shortage of a radioresource allocated to a user equipment being served by own cell but theshortage of the radio resource allocated to a user equipment thatperforms communication for a service having a high priority order orperforms communication requiring high QoS. In this manner, the MBSFNsubframe configuration can be more preferential than radio resourceallocation to a user equipment having a low priority order or a low QoS,and interference to another cell can be reduced.

The base station to which interference occurs as a problem may performnotification of information related to a priority order of a service ofa interfered user equipment being served thereby or information relatedto the QoS together with a request message of the MBSFN subframeconfiguration. The base station that receives a request notification ofthe MBSFN subframe configuration can judge whether or not the MBSFNsubframe configuration is performed on the basis of the information.

As a specific example of an interface used to perform notification ofrejection of the MBSFN subframe configuration, the methods disclosed inthe specific examples (1) to (3) of the interface used for notificationto a neighbor cell in the first modification of the first embodimentdescribed above can be applied. The information representing that theMBSFN subframe configurations is rejected is included in a signalingmessage used on each interface or a signaling message to performnotification of the rejection is newly set to perform notification byusing the interfaces.

The base station that receives a request notification of the MBSFNsubframe configuration cannot recognize time until the base stationserving as a request source requires the MBSFN subframe configuration.In this case, when the base station configures the MBSFN subframe on thebasis of the configuration request of the MBSFN subframe, the basestation cannot determine the time until the configuration of the MBSFNsubframe need to be maintained. Even when the MBSFN subframeconfiguration is unnecessary in such a case where the user equipmentthat is interfered by the base station serving as a request source endscommunication, the base station that receives the request consequentlycontinues the MBSFN subframe configuration. This wastes resources tocause a reduction in capacity of a cell or a decrease in communicationspeed. In order to solve the problem, a base station that performsnotification of a request of an MBSFN subframe configuration may performnotification representing that the request is ended.

The base station that performs notification of the request of the MBSFNsubframe configuration judges whether or not the base station requests aneighbor base station of the MBSFN subframe configuration as abovedescribed. When the base station judges that the MBSFN subframeconfiguration is not requested, notification representing the request isended is performed. The notification representing that the request isended may be performed to the base station that performs notification ofa request of an MBSFN subframe configuration. The base station thatperforms notification of a request of an MBSFN subframe configurationmay judge whether or not a neighbor base station is requested of anMBSFN subframe configuration, regularly, periodically, or by using as atrigger a report of a measurement result from a user equipment beingserved thereby.

The base station that receives a request end notification of the MBSFNsubframe configuration inactivates the MBSFN subframe configurationconfigured on the basis of the request end notification. Morespecifically, a subframe configured as an MBSFN subframe is configuredto be used in normal uni-cast communication.

In this manner, the base station can improve efficiency of using aresource to make it possible to increase a capacity of a cell orincrease a communication speed.

The base station that receives a request of an MBSFN subframeconfiguration or a notification representing that the request is endedmay notify a base station serving as a request source that the requestor the request end notification is received. Alternatively, notificationrepresenting that an MBSFN subframe is configured based on the requestnotification or notification representing that the MBSFN subframeconfiguration is inactivated on the basis of the request endnotification may be performed. In this manner, the base station servingas the request source can clearly recognize a configuration state of anMBSFN subframe of a base station serving as a request destination andcan correctly judge whether or not the base station serving as therequest source performs notification of a request of an MBSFN subframeconfiguration or notification of a request end. For this reason, thesystem can be prevented from being erroneously operated, and a stablecommunication system can be provided.

In the above description, the base station that receives a request endnotification of the MBSFN subframe configuration inactivates the MBSFNsubframe configuration configured on the basis of the request endnotification. Unless the base station that configures an MBSFN subframereceives the request end notification, the MBSFN subframe configurationcannot be inactivated. In this case, since resource allocation cannot beperformed when communication with a user equipment being served by owncell is required to be preferentially performed, a problem that makescommunication impossible is posed. In order to solve the problem, a basestation that configures MBSFN subframe may determine to end the MBSFNsubframe configuration. The base station that has determined to end theMBSFN subframe configuration inactivates the MBSFN subframeconfiguration. The base station that inactivates the MBSFN subframeconfiguration may notify a base station serving as a request source ofthe MBSFN subframe configuration that the MBSFN subframe configurationis inactivated.

As a judgment condition for inactivating the MBSFN subframeconfiguration, whether or not a radio resource allocated to a userequipment being served by own cell comes short may be used. The shortageof the radio resource, as described above, may not be the shortage of aradio resource allocated to a user equipment being served by own cellbut the shortage of the radio resource allocated to a user equipmentthat performs communication for a service having a high priority orderor performs communication requiring high QoS.

In this manner, the base station that configures the MBSFN subframe canallocate a resource when communication with a user equipment beingserved by own cell is required to be preferentially performed, and aservice can be provided to the user equipment being served by own cell.

When the base station that receives the request notification of theMBSFN subframe configuration continuously uselessly configures the MBSFNsubframe, a useless resource, consequently, a reduction in capacity of acell or a decrease in communication speed is caused. Another method ofsolving the problem is disclosed. A period in which an MBSFN subframe isconfigured is limited. The base station inactivates the MBSFN subframeconfiguration a predetermined period after the MBSFN subframe isconfigured. The predetermined period may be used as a timer. Thepredetermined period may be statically determined in advance,semi-statically determined or dynamically determined.

When the predetermined period is statically determined, thepredetermined period may be determined as a specification. Thepredetermined period can be recognized by all the base stations. Sincesignaling to notify the base station of the predetermined period is notrequired, an amount of signaling can be reduced.

When the predetermined period is semi-statically determined, thepredetermined period may be determined by the MME. The MME may notifyeach of the base station of the predetermined period. The MME may notifythe base station of the predetermined period by the S1 message throughthe S1 interface. When the MME notifies the HeNB, the MME may performnotification in registration of the HeNB.

The predetermined period is semi-statically determined, thepredetermined period may be determined by the base station. The basestation broadcasts it as system information. A base station thatrequests an MBSFN subframe configuration must recognize an MBSFNsubframe configuration period of the base station that configures theMBSFN subframe. As this method, a method in which the base station thatrequests the MBSFN subframe configuration receives system information tobe broadcasted from a base station that causes interference, i.e., abase station serving as a request destination of the MBSFN subframeconfiguration or a method of receiving the system information from auser equipment being served by the base station that requests the MBSFNsubframe configuration is used. In the method of receiving from the userequipment, the user equipment may receive the system informationbroadcasted from a base station that causes interference to acquire thepredetermined period and notify a serving cell of the predeterminedperiod together with a measurement report. In this manner, thepredetermined period in which the MBSFN subframe is configured can bedetermined depending on a status of use of a radio resource of each basestation.

When the predetermined period is dynamically determined, a base stationthat receives request notification of the MBSFN subframe configurationmay perform the notification to a base station serving as a requestsource. As a response to the request notification of the MBSFN subframeconfiguration, the notification of the predetermined period may beperformed. In this manner, the base station can determine thepredetermined period in which the MBSFN subframe is configured dependingon a status of use of the radio resource at a time when the base stationreceives the MBSFN subframe configuration request.

The base station that configures the MBSFN subframe inactivates theMBSFN subframe after the predetermined period has elapsed. However, inthe predetermined period, when the MBSFN subframe configuration requestis received, the MBSFN subframe may be configured in the predeterminedperiod from the time. When the predetermined period is used as a timer,a base station that receives an MBSFN subframe configuration requeststarts the timer by using, as start time, time when the MBSFN subframeis configured. When the time for the timer runs out, the MBSFN subframeconfiguration is inactivated to reset the timer. When the MBSFN subframeconfiguration request is received before the time for the timer runsout, the timer may be restarted from the time.

The base station that performs notification of the MBSFN subframeconfiguration request may perform processing based on the predeterminedperiod. For example, from time when the notification of the MBSFNsubframe configuration request is performed or from time when anotification representing that the MBSFN subframe is configured based onthe request notification is received, after the predetermined period haselapsed, a configuration request is performed if the configurationrequest is necessary again. The configuration request may be performedagain before the predetermined period has elapsed. When thepredetermined period is used as a timer, the timer may be started byusing, as start time, time when the notification of the MBSFN subframeconfiguration request is performed or time when a notificationrepresenting that the MBSFN subframe is configured based on the requestnotification is received. When the time for the timer runs out, thetimer is reset and a configuration request is performed if theconfiguration request is necessary again. The configuration request maybe performed again before the time for the timer runs out. In this case,the timer may be restarted by using, as start time, time whennotification of the configuration request is performed again or timewhen a notification representing that the MBSFN subframe is configuredagain based on the configuration request is received. When notificationof an MBSFN subframe configuration request end is performed before thetime for the timer runs out, the timer may be reset when thenotification of the request end is performed or when notificationrepresenting that the MBSFN subframe configuration is inactivated on thebasis of the request notification.

When the time management is performed as described above, even in thebase station that performs notification of the MBSFN subframeconfiguration request or the base station that receives the MBSFNsubframe configuration request, efficiency of using a resource can beimproved, a capacity of each cell and a communication speed can beincreased.

The method disclosed in the embodiment can also be applied to a casewhere an MME configures an MBSFN subframe (will be described later).Processing performed by a base station that configures an MBSFN subframeand signaling performed with a base station that configures an MBSFNsubframe may be alternatively performed by the MME.

Sixth Embodiment

The embodiments and the modifications described above disclose themethod of causing a base station to configure an MBSFN subframe. The MMEmay configure the MBSFN subframe without causing the base station toconfigure the MBSFN subframe. In other words, the MME may have afunction of configuring an MBSFN subframe. The MME notifies one or aplurality of base stations of the MBSFN subframe configuration. A basestation serving as a notification object may be a base station beingserved by another MME. In this case, notification of the MBSFN subframeconfiguration is performed through the other MME. The base station thatreceives the MBSFN subframe configuration configures an MBSFN subframeaccording to the MBSFN subframe configuration. All the base stationsthat receive the MBSFN subframe configuration need not configure MBSFNsubframes according to the MBSFN subframe configuration. When the MBSFNsubframe configuration is recognized, the MBSFN subframe may be used inother applications.

For example, when the MBSFN subframe is used to avoid downlinkinterference between cells, the MME notifies a normal eNB (macro cell)that gives interference and a low transmission power local node thatreceives interference of an MBSFN subframe configuration. A normal eNB(macro cell) that gives interference configures an MBSFN subframe, and alow transmission power local node that is interfered by the eNB uses theMBSFN subframe in uni-cast communication. The resource of the MBSFNsubframe is scheduled for a user equipment to which interference occursas a problem to make it possible to reduce inter-cell downlinkinterference.

The example described above shows the case where interference betweenthe macro cell and the low transmission power local node occurs.However, the present invention can be similarly applied to not only theinterference but also interference between normal base stations orinterference between low-power local nodes. The inter-cell downlinkinterference can be avoided. In this manner, in place of the basestation, the MME configures the MBSFN subframe to make it easy toconfigure the same MBSFN subframes in a plurality of base stations.

Each of the number of base stations that give interference and thenumber of base stations that are interfered may be one or more.

As a method of notifying a plurality of base stations of an MBSFNsubframe configuration, a technique (conventional technique) that causesan MCE to configure an MBSFN subframe to notify the plurality of basestations of the MBSFN subframe is used.

However, in this case, the plurality of base stations serving asnotification targets are all base stations that are present in one MBSFNarea. Consequently, the MBSFN subframes are configured to all the basestations that are present in one MBSFN area managed by the MCE. Thus,when the MCE configures an MBSFN subframe for not only multi-celltransmission but also avoiding inter-cell downlink interference,regardless of a base station to which interference occurs as a problem,all the base stations that are present in the MBSFN area are notified ofthe MBSFN subframe configuration. This cause useless signaling. Wheninterference avoidance is required to be performed with a base stationthat is not present in the MBSFN area, in order to prevent the basestation that is not present in the MBSFN area is not notified of theMBSFN subframe configuration, and thus interference avoidance with thebase station becomes impossible. Furthermore, the HeNB may not beconnected to the MCE. In this case, when the MCE configures an MBSFNsubframe, the HeNB cannot be directly notified of the MBSFN subframeconfiguration.

As a method of solving the problem, the MCE may notify the HeNB of theMBSFN subframe configuration through the MME. The MCE notifies the MMEof the MBSFN subframe configuration by using the M3 interface, and theMME notifies the HeNB of the MBSFN subframe configuration by using theS1 interface. In this manner, the HeNB that does not have a directinterface with the MCE can be notified of the MBSFN subframe configuredby the MCE.

However, according to the method, signaling the notification of which istemporarily performed through the MME increases.

When the method in which the MME configures an MBSFN subframe is used,the problems can be solved. More specifically, when the MME configuresthe MBSFN subframe, regardless of a base station in the MBSFN area, abase station to which interference occurs as a problem can be notifiedof the MBSFN subframe configuration. A base station that does not belongto the MBSFN area can also be notified of the MBSFN subframeconfiguration. Furthermore, the MCE needs not to notify the MME of theMBSFN subframe configuration, a signaling amount is not increased.

Thus, when a base station except for a base station belonging to oneMBSFN area needs to be notified of an MBSFN subframe, the MMEadvantageously configures MBSFN subframe.

As described above, since a cell using the MBSFN subframe or a cell thatperforms notification of the MBSFN subframe configuration can beflexibly configured, the MBSFN subframe is advantageously used inanother application except for multi-cell MBMS transmission.

As a method of selecting a neighbor cell that performs notification ofan MBSFN subframe configured by the MME, a method of selecting aneighbor cell used when a base station configures an MBSFN subframe asdescribed above can be applied.

As a method of adjusting an MBSFN subframe performed in the MCE and amethod of configuring an MBSFN subframe performed in the MME, themethods disclosed in from the second modification of the firstembodiment to the fifth modification of the first embodiment can beapplied. In place of the eNB, the MME may be used. Notification betweenthe MME and the MCE may be performed by using the M3 interface. In thismanner, the MCE can adjust the MBSFN subframe (MCE) by using the MBSFNsubframe information configured by the MME, and the MME can configurethe MBSFN subframe by using information or the like of the priorityorder of the MBSFN subframes notified from the MCE.

As the MBSFN subframe configured by the MME, the methods disclosed infrom the second embodiment to the second modification of the secondembodiment may be applied. In this manner, the same effect as describedabove can be obtained.

When the MME configures the MBSFN subframe to a base station that doesnot belong to an MBSFN synchronization area, a base station that is notconnected to the MCE or a base station that does not receivenotification of the MBSFN subframe configuration from the MCE, themethod disclosed in the third embodiment may be applied. The M3interface may be used for the notification of the MBSFN subframeconfiguration from the MME to the MCE, and the S1 interface may be usedfor the notification of the MBSFN subframe configuration from the MME tothe eNB. In this manner, the same effect as described above can beobtained.

When an MBSFN subframe is used to avoid downlink interference betweenthe cells, a base station to which interference occurs as a problem mayrequest the MME to configure an MBSFN subframes for avoiding downlinkinterference. The MME that receives the request configures an MBSFNsubframe and notifies the neighbor base station of the MBSFN subframeconfiguration. The S1 interface may be used for the notification. Therequest is included in a signaling message used on the S1 interface, ora signaling message for the request is newly set to performnotification. In addition to the notification of the request,notification of an identifier (cell identifier) of a base stationserving as a source of the request, a cell identifier of own cell, or arequested resource may be performed. Notification of combinations of theidentifiers and the resource may be performed. As the identifier of thebase station serving as a destination or a cell identifier of own cell,a CGI, a PCI or the like may be used. As a specific example of therequested resource, the number of MBSFN subframes may be used. An MMEthat receives notification of the requested resource can use thenotification as information for judgment used when the number of MBSFNsubframes is configured.

As a specific example of a judgment whether or not the base stationrequests a neighbor base station of the MBSFN subframe configuration anda method of selecting a neighbor base station, the above described samemethods used when a base station to which interference occurs as aproblem requests the neighbor base station of the MBSFN subframeconfiguration can be applied. The MME that receives the request from thebase station to which interference occurs as a problem configures anMBSFN subframe for avoiding inter-cell downlink interference. The MMEthat configures the MBSFN subframe notifies neighbor cells of theconfiguration.

The MME may discriminate a base station that performs the MBSFN subframeconfiguration from a base station that performs only notificationwithout performing the configuration. The base station that givesinterference may perform an MBSFN subframe configuration, and the basestation that receives interference may perform only the notification ofthe MBSFN subframe configuration.

Information representing whether or not the MBSFN subframe configurationis performed may be configured. The MME may notify the base station ofthe information. In this manner, the MME can discriminate a base stationthat causes the base station that performs a notification of an MBSFNsubframe configuration to perform the MBSFN subframe configuration fromother base stations.

For example, the information representing whether or not the MBSFNsubframe configuration is performed is used as an indicator. Forexample, when 1-bit information is “1”, the MBSFN subframe may beconfigured. When the 1-bit information is “0”, the MBSFN subframe neednot be configured. The base station that gives interference may benotified of an indicator set to “1”, and the base station that receivesinterference may be notified of an indicator set to “0”.

The base station that receives the MBSFN subframe configuration andinformation representing that MBSFN subframe configuration is performedfrom the MME configures an MBSFN subframe according to the MBSFNsubframe configuration. The base station notifies the user equipmentbeing served thereby of the configuration. The base station thatreceives an MBSFN subframe configuration and information representingthat the MBSFN subframe configuration is not performed, on the basis ofthe MBSFN subframe configuration, schedules a resource of an MBSFNsubframe for uni-cast communication to a user equipment to whichinterference occurs as a problem. As the user equipment to whichinterference from the base station occurs as a problem, a user equipmentthat performs notification of a measurement report representing thatreception quality from the base station exceeds a predeterminedthreshold value may be used. In this manner, the interference from thebase station can be avoided.

When a method disclosed in the embodiment is applied, inter-celldownlink avoidance using the MBSFN subframe by the MME can be moredynamically realized.

While the LTE system (E-UTRAN) and the LTE advanced (LTE-Advanced) havemainly been described in the present invention, the present invention isapplicable to the W-CDMA system (UTRAN, UMTS).

The invention claimed is:
 1. A mobile communication system comprising:at least one user equipment; a plurality of base stations that performradio communication with the at least one user equipment; and a radionetwork controller that controls the plurality of base stations, whereinsaid radio network controller indicates a resource that is a radioresource for transmitting to said user equipment a reference signal lessfrequently than normal to said base stations, the reference signal beingtransmitted to measure power, a base station of the plurality of basestations designates, in addition to the resource indicated by said radionetwork controller, a resource that is a radio resource for transmittingsaid reference signal to said user equipment less frequently thannormal, said base station transmits said reference signal to said userequipment less frequently than normal in the resource indicated by saidradio network controller and the resource additionally designated bysaid base station itself, and said user equipment receives saidreference signal from said base station less frequently than normal inthe resource indicated by said radio network controller and the resourceadditionally designated by said base station.
 2. A base station thatperforms radio communication with user equipment in response to acontrol by a radio network controller, wherein said radio networkcontroller indicates a low-frequency resource that is a radio resourcefor transmitting to said user equipment a reference signal lessfrequently than normal to said base station, the reference signal beingtransmitted to measure power, the base station designates, in additionto the low-frequency resource indicated by said radio networkcontroller, a low-frequency resource that is a radio resource fortransmitting said reference signal to said user equipment lessfrequently than normal, and said base station transmits said referencesignal to said user equipment less frequently than normal in thelow-frequency resource indicated by said radio network controller andthe low-frequency resource additionally designated by said base stationitself.
 3. The base station according to claim 2, wherein said basestation notifies a neighbor base station of the low-frequency resourceadditionally designated by said base station itself.
 4. The base stationaccording to claim 2, wherein said base station notifies said radionetwork controller of the low-frequency resource additionally designatedby said base station itself.
 5. The base station according to claim 2,wherein said base station additionally designates the low-frequencyresource in addition to the low-frequency resource indicated by saidradio network controller depending on an operation state.
 6. The basestation according to claim 5, wherein, when said base station operatesin an energy-saving mode having an operation power lower than a normaloperation power, said base station additionally designates thelow-frequency resource in addition to the low-frequency resourceindicated by said radio network controller.
 7. The base stationaccording to claim 2, wherein said low-frequency resource is a subframeto transmit multimedia data of a radio frame.
 8. A radio networkcontroller that controls the plurality of base stations that performradio communication with user equipment, wherein said radio networkcontroller indicates a low-frequency resource that is a radio resourcefor transmitting to said user equipment a reference signal lessfrequently than normal to said base stations, the reference signal beingtransmitted to measure power, and said radio network controller changesthe low-frequency resource indicated to said base station on the basisof a low-frequency resource additionally designated by said basestation.
 9. The radio network controller according to claim 8, whereinsaid low-frequency resource is a subframe to transmit multimedia data ofa radio frame.
 10. A user equipment that performs radio communicationwith a base station controlled by a radio network controller, whereinsaid user equipment receives a reference signal less frequently thannormal in a resource indicated by said radio network controller and aresource additionally designated by said base station, the referencesignal being received to measure power, said user equipment performs areception Dower measurement to determine a reception quality of signalsfrom the base stations, the user equipment determines whether to connectto the base station based on the reception quality determined, and theuser equipment connects to the base station based on a result of thedetermination of reception quality, wherein the resource indicated bysaid radio network controller is changed to another resource based onthe additionally designated resource by the base station, and thechanged resource is indicated to the user equipment.